Asymmetric synthesis of peptides

ABSTRACT

A process comprising substitution of an acceptor molecule comprising a group —XC(O)— wherein X is O, S, or NR 8 , where R 8  is C 1-6  alkyl, C 6-12  aryl or hydrogen, with a nucleophile, wherein the acceptor molecule is cyclised such that said nucleophilic substitution at —XC(O)— occurs without racemisation, is provided. This process has particular application for the production of a peptide by extension from the activated carboxy-terminus of an acyl amino acid residue without epimerisation.

RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.12/066,727, filed Mar. 13, 2008, which is the U.S. national stage ofInternational Application No. PCT/GB05/03797, which designated theUnited States and was filed on Sep. 30, 2005, published in English,which claims priority under 35 U.S.C. §119 or 365 to United Kingdom,Application No. 0518667.1, filed 13 Sep. 2005. The entire teachings ofthe above applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a novel process for peptide synthesis,by the addition of amino acids to the activated C-terminus of a peptidechain. Peptide synthesis is central to the manufacture of many drugs andmedicaments. Peptides or derivatives thereof are used for the treatmentof many disorders from antibiotics to anticancer agents. Thereforeimproving peptide synthesis and the yield of peptide produced bychemical synthesis has been the focus of much research in recent years.

Chemical synthesis of proteins or peptides has been a particular focusin the art. The chemical synthesis of proteins or peptides allows theproduction of purified peptides of specific amino acid sequence. It alsoallows the production of truncated sequences of amino acids and allowsthe introduction of non-natural amino acid derivatives.

Proteins are produced in nature by the stepwise condensation of aminoacid monomers on a ribosome. Synthesis of the protein begins from theN-terminal residue and grows towards the C-terminus. The conventionalapproach to peptide synthesis has concentrated on extension at theN-terminus of a growing peptide. This approach forms the basis ofconventional solid phase peptide synthesis. Peptide synthesis solely byextension from the N-terminus is limiting as it renders any peptidesynthesis lineal in nature, rather than convergent. This can severelyincrease overall length of synthesis, increase operational time anddecrease overall yield with consequent possibilities for the loss ofstereochemical fidelity.

To overcome the problems associated with N-terminal extension of apeptide, it could be envisaged that the synthesis could instead provideextension of a peptide from the C-terminal. However, attempts at peptidesynthesis in the N to C direction have been generally unsuccessful dueto epimerisation of the carboxy-terminal amino acid residue. This is dueto the tendency of carboxy-terminal-activated acylamino acids andpeptides to form oxazolones. As illustrated below, the formation of theoxazolone allows rapid racemisation of the alpha-position of theterminal amino acid residue of the acyl amino acid or peptide.

This racemisation prevents the production of stereochemicallyhomogeneous peptides by C-terminus extension.

It will be appreciated that the production of isomerically purecompounds is a particular requirement in the art. Any method whichresults in the production of a mixture of isomers will require the useof time consuming and expensive purification steps to separate theisomers. Chiral compounds which are administered to humans or animalsare usually required in enantiomerically pure form. The presence ofunwanted isomers even in low concentrations can reduce the potency ofthe compound and can produce unwanted and in some cases disastrous sideeffects. The incorporation of an unwanted enantiomer into a peptidechain (for example the incorporation of a D-amino acid into a peptidecomposed of L-amino acids) may disrupt the folding and/or 3D shape ofthe peptide, thus resulting in a peptide which may have unpredictablebinding activities and/or biological properties. The production ofenantiomerically pure peptides is therefore of paramount importance.

Various attempts have been made to overcome this problem. Iorga, B andCampagne, J-M (2004, Synlett 10, 1826-1828) attempted to reduce thedegree of epimerisation by improving the rate of peptide bond formationover the rate of oxazolone formation so that peptide bond formation wasthe predominant reaction. However, this method does not entirely preventthe formation of the oxazolone and therefore epimerisation at thecarboxy-terminal activated amino acid residue occurs. Native chemicalligation has been developed to overcome problems of carboxy-terminalextension but is ordinarily restricted to couplings in which theamino-terminal partner is an assisting cysteine residue and is notapplicable to general techniques of automated solid phase peptidesynthesis. The application of native chemical ligation to otheramino-terminal amino acids has had very limited success.

The present invention provides a new method of producing a peptide byextension from the activated carboxy-terminus of an acyl amino acidresidue. This new method overcomes the problems of epimerisation of theterminal amino acid residue during the coupling step. The presentinvention therefore allows the production of peptides by a convergentapproach and provides a new method for the production of potentiallybiologically important compounds instead of the linear repetitive aminoterminal extension approach currently used.

The first aspect of the present invention provides a process comprisingsubstitution of an acceptor molecule comprising a group —XC(X)—(preferably —X(CO)—) wherein each X is independently O, S or NR⁸, whereR⁸ is hydrogen, aliphatic group or an aromatic group, preferablyhydrogen, C₁₋₆ alkyl, C₆₋₁₂ aryl, with a nucleophile, wherein theacceptor molecule is cyclised such that said nucleophilic substitutionat —XC(X)— occurs without racemisation. The acceptor molecule ispreferably a cyclised amino acid or derivative thereof. In particular,the acceptor molecule is a compound of formula (II):

wherein each X is O, S, or NR⁸, where R⁸ is as defined above;R² is independently selected from an aliphatic group, such as a C₁₋₁₀branched or straight chain alkyl group, or an aromatic group, such asC₅₋₁₂ heteroaryl group or C₆₋₁₂ aryl group, each optionally substitutedwith a group including, for example, OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³,CON(R¹³)₂, SO₂R¹², SO₃R¹², phenyl, imidazolyl, indolyl, hydroxyphenyl orNR¹³C(═NR¹³)N(R¹³)₂;R³ is as defined for R² or is hydrogen,or a group

or a group

a group —C(R^(1′))(R⁹)—N(R¹⁰)(R¹¹);wherein R^(1′) is independently selected from an aliphatic group such asC₁₋₁₀ branched or straight chain alkyl group, an aromatic group, such asC₅₋₁₂ heteroaryl group or C₆₋₁₂ aryl group, each optionally substitutedwith a group such as OR¹³SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, SO₂R¹²,SO₃R¹², phenyl, imidazolyl indolyl, hydroxyphenyl orNR¹³C(═NR¹³)N(R¹³)₂;wherein when Y is NR⁸, R⁸ and R^(1′) can together form a 4 to 7 memberedring, optionally substituted with a group such as CO₂R¹³, OR¹³, SR¹³,N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, C₁₋₁₀ alkyl or C₆₋₁₂ aryl, wherein said ringcan be fully, partially or unsaturated, and wherein the ring may containone or more additional heteroatoms selected from O, S or N;R¹² is hydrogen, C₁₋₆ alkyl C₆₋₁₂ aryl or N(R¹³)₂, wherein eachoccurrence of R¹³ is independently hydrogen, C₁₋₆ alkyl or C₆₋₁₂ aryl,and R^(4′) is a carboxyl protecting group or hydrogen;R⁹ and R¹⁰ are independently hydrogen or a group as defined for R^(1′);R¹¹ is hydrogen or an amino protecting group preferably selected from abenzyloxycarbonyl group, a t-butoxycarbonyl group, a2-(4-biphenylyl)-isopropoxycarbonyl group, a fluorenylmethoxycarbonylgroup, a triphenylmethyl group and/or a 2-nitrophenylsulphenyl group;or R⁹ and R¹⁰ or R¹⁰ and R¹¹ or R^(1′) and R¹⁰ or two R¹³ can togetherform a 4 to 7 membered ring, optionally substituted with a group such asCO₂R¹³, OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, C₁₋₁₀ alkyl or C₆₋₁₂aryl, wherein said ring can be fully, partially or unsaturated, andwherein the ring may contain one or more additional heteroatoms selectedfrom O, S or N;Y is O, S or NR⁸, where R⁸ is as defined above;YR^(4′) is R³;R⁵ is an aromatic group such as C₆₋₁₂ aryl, C₅₋₁₂ heteroalkyl or analiphatic group such as C₁₋₈ branched or straight chain alkyl optionallysubstituted with a group such as OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂,phenyl, imidazolyl, indolyl, hydroxyphenyl or NR¹³C(═NR¹³)N(R¹³)₂ or alinker for attachment of formula (II) to a resin or a linked resin;n is 0, 1, 2 or 3 and m is an integer, such as an integer selected from1-100.

The nucleophilic substitution of the acceptor molecule preferably occurswithout epimerisation.

Preferably, the process is carboxy terminal extension of an acceptormolecule, for example an amino acid or peptide. The invention thereforeprovides a process for the synthesis of a peptide or a peptide analog bycarboxy terminal extension, by the addition of a nucleophile to anacceptor molecule such as a compound of formula (II).

There is further provided a process for the production of a compound offormula (I)

comprising reaction of a compound of formula (II) or (II′) (above)

with a compound of formula (III)HY—R⁷  (III)wherein the variables are defined as above:preferably X is O, S, or NR⁸, where R⁸ is as defined above, Y is O, S orNH;R² is independently selected from a C₁₋₁₀ branched or straight chainalkyl group, C₅₋₁₂ heteroaryl group or C₆₋₁₂ aryl group, optionallysubstituted with OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, SO₂R¹², SO₃R¹²,phenyl, imidazolyl, indolyl, hydroxyphenyl or NR¹³C(═NR¹³)N(R¹³)₂;R³ is as defined for R² or is hydrogen, or a group

or a group —C(R^(1′))(R⁹)—N(R¹⁰)(R¹¹);wherein R^(1′) is hydrogen or as defined from R¹ below; Y is as definedabove and R⁴ is as defined for R⁴ below;R¹² is hydrogen, C₁₋₆ alkyl, C₆₋₁₂ aryl or N(R¹³)₂, wherein eachoccurrence ofR¹³ is independently hydrogen, C₁₋₆ alkyl or C₆₋₁₂ aryl,R⁹ and R¹⁰ are independently hydrogen or a group as defined for R^(1′);or R⁹ and R¹⁰ can together form a 4 to 7 membered ring, optionallysubstituted with CO₂R¹³, OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, C₁₋₁₀alkyl or C₆₋₁₂ aryl, wherein said ring can be fully, partially orunsaturated, and wherein the ring may contain one or more additionalheteroatoms selected from O, S or N,R¹¹ is hydrogen or an amino protecting group preferably selected from abenzyloxycarbonyl group, a t-butoxycarbonyl group, a2-(4-biphenylyl)-isopropoxycarbonyl group, a fluorenylmethoxycarbonylgroup, a triphenylmethyl group and/or a 2-nitrophenylsulphenyl group;R⁵ is an aromatic group, such as C₅₋₁₂ aryl, C₅₋₁₂ heteroalkyl or analiphatic group, such as C₁₋₈ branched or straight chain alkyloptionally substituted with OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³, CO N(R¹³)₂,phenyl, imidazolyl, indolyl, hydroxyphenyl orNR¹³C(═NR¹³)N(R¹³)₂ or a linker for attachment of formula (II) to aresin or a linked resin; R⁶ is hydrogen or

wherein R⁵ and X are as defined above;R⁷ is a chiral, substituted methylene, such as a group

or is independently selected from an aliphatic group such as a C₁₋₁₀branched or straight chain alkyl group or an aromatic group, such as aC₆₋₁₂ aryl group, optionally substituted with OR¹³, SR¹³, N(R¹³)₂,CO₂R¹³, CON(R¹³)₂, SO₂R¹², SO₃R¹², phenyl, imidazolyl, indolyl,hydroxyphenyl or NR¹³C(═NR¹³)N(R¹³)₂);or wherein R⁷ and Y together form a 4 to 7 membered ring, optionallysubstituted with a group such as OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂,SO₂R¹², SO₃R¹², phenyl, imidazolyl, indolyl, hydroxyphenyl orNR¹³C(═NR¹³)N(R¹³)₂, wherein said ring can be fully, partially orunsaturated, and wherein the ring may contain one or more heteroatoms inaddition to Y, selected from O, S or N;wherein R¹ is R^(1′) or is independently selected from an aliphaticgroup such as C₁₋₁₀ branched or straight chain alkyl group, or anaromatic group such as C₅₋₁₂ heteroaryl group or C₆₋₁₂ aryl groupoptionally substituted with a group such as OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³,CON(R¹³)₂, SO₂R¹², SO₃R¹², phenyl, imidazolyl, indolyl, hydroxyphenyl orNR¹³C(═NR¹³)N(R¹³)₂;and R⁴ is R^(4′) or a carboxyl protecting group or hydrogen; n is 0, 1,2 or 3 and m is an integer such as a value selected from 1-100 and whenn=0, R⁶ is H.

The inventors have surprisingly found that activation of an amino acidor peptide via a cyclic compound as exemplified in formula (II) preventsthe formation of an oxazolone thereby allowing the condensation of acompound of formula (III) without concommitant epimerisation. Theinvention therefore provides peptides via C-terminus extension, saidpeptides being produced in an enantiomerically and diastereochemicallypure form.

The use of activated cyclic N-acyl amino acids, peptides or derivativesthereof eliminates oxazolone formation and associated epimerisation. Theuse of cyclic activated intermediates in the present invention providesan improved method of peptide synthesis via carboxy-terminal extension.

Therefore, rather than merely reducing the probability of epimerisationoccurring, as has been attempted in the prior art, the process of thepresent invention does not permit epimerisation and therefore guaranteesthe production of a peptide of correct stereochemistry as the activatedcarboxyl terminus is held in a cyclic template such that the adjacentamide cannot form the oxazolone.

In accordance with usual practice, * denotes a stereocenter (asymmetriccenter). Where a compound contains a stereocenter (whether marked in thepresent application with * or not) the stereochemistry of the asymmetriccenters may be in the R or S configuration. The compounds of the presentapplication can be provided in enantiomerically pure form or as amixture of isomers (including a racemic mixture). Preferably, thecompounds of the present inventions are provided in an enantiomericallypure form. The present invention allows maintenance of the desiredstereochemistry throughout the synthetic pathway. Thus wherein Y is NH,the amino acids to be attached may be of L or D configuration asrequired.

Preferably R¹ and R² are independently selected from C₁₋₄ branched orstraight chain alkyl optionally substituted with OR¹³, SR¹³, N(R¹³)₂,CO₂R¹³, CON(R¹³)₂, phenyl, imidazolyl, indolyl, hydroxyphenyl orNR¹³C(═NR¹³)N(R¹³)₂, preferably optionally substituted with OH, SH, NH₂,CO₂H, CONH₂, phenyl, imidazolyl, indolyl, hydroxyphenyl or NH(C═NH)NH₂.

More preferably, R and R are independently selected from C₁ alkyloptionally substituted with OH, SH, CO₂H, CONH₂, phenyl, imidazolyl,indolyl or hydroxyphenyl; C₂ alkyl optionally substituted with OH, CO₂H,CONH₂ or SCH₃; C₃ alkyl optionally substituted with NHC(═NH)NH₂ or C₄alkyl optionally substituted with NH₂.

The integer, m is preferably 1-50, more preferably 1 to 30, mostpreferably 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19 or 20. The integer n is preferably 0 or 1.

When X is NR, R is preferably Ci⁻⁴ alkyl more preferably methyl, ethyl,n-propyl, iso-propyl, n-butyl or tert-butyl, phenyl, naphthyl,anthracenyl or phenanthracenyl, more preferably phenyl or hydrogen.

R³ may also be substituted pipecolic acid or derivative thereof,α-alkoxy-α-amino acids, α,α-diamino acids, β-substituted dehydroaminoacids, canavanine, cysteinesulphonamide, homocysteinesulphonamide,γ,δ-unsaturated amino acids, substituted 4-hydroxyprolines,4-hydroxtyornlithines, imino sugars, Fmoc-BPC—OH, Fmoc-TPG-OH andFmoc-CAA-OH, or (5)-3,5-dihydroxyphenylglycine.

It will be appreciated by a person skilled in the art that amino acids,hydroxy acids and derivatives thereof contain functional groups whichrequire protection. In particular it is known in the art to protect theamino terminus, the carboxyl terminus and/or the side chains of an aminoacid or peptide (for example wherein R¹ or R² is CH₂CO₂H or CH₂CH₂OH).Examples of such protection are well known in the art. In particular theamino terminus of an amino acid may be protected by one or more of abenzyloxycarbonyl group, a t-butoxycarbonyl group, a2-(4-biphenylyl)-isopropoxycarbonyl group, a fluorenylmethoxycarbonylgroup, a triphenylmethyl group and/or a 2-nitrophenylsulphenyl group.The carboxyl group can be protected by one or more of an ester groupespecially a methyl, ethyl, benzyl, t-butyl or phenyl ester. Thus R⁴ ispreferably methyl, ethyl, benzyl, t-butyl or phenyl.

Conditions for the removal of the protecting groups discussed above arewell known in the art. The protecting groups may be removed after eachcoupling reaction (for example, the carboxyl protection) oralternatively at the end of the synthesis (for example, the side chainprotection and/or the N-terminal group).

In a particular feature of the first aspect, the invention provides aprocess for production of a compound of formula (Ia)

comprising reacting a compound of formula (IIa) (above)with a compound of formula (III) HY—R⁷;Wherein the groups Y, X, R², R³, R⁵, and R⁷ are as defined above.In an alternative feature of the first aspect, the invention provides aprocess for production of a compound of formula (Ib)

comprising reacting a compound of formula (IIb)

with a compound of formula (III) HY—R⁷wherein the groups Y, X, R², R³, R⁵ and R⁷ are as defined above forcompounds (I), (II) and (III).

The N and the terminal ester of formula (I), (Ia) or (Ib) can beunmasked by processes known in the art, for example, sodium liquidammonia in the presence of an alcohol when R¹=phenyl and R⁴=t-butyl.Alternatively, the ester can be further derivatized, including forexample, amidation.

The nucleophilic substitution of the acceptor molecule of the firstaspect of the invention can be carried out using reaction conditionsknown in the art. In some circumstances, for example where thenucleophile and/or the acceptor molecule are sterically hindered it maybe necessary for example to use high pressure such as around 19-20 bar,and/or longer reaction times such as 12-72 hours, preferably 24-48hours. Alternatively, the reaction can be carried out in the presence ofa reagent such as AlMe₃. When the substitution is carried out on thesolid phase, the reaction can be promoted by the use of an excess ofnucleophile.

The invention further relates to a process for the production of acompound of formula (II) (above) by the reaction of a compound offormula (IV)

with a compound of formula (V) Z—CO—R³wherein Z is any substituent capable of being involved in peptide bondformation preferably hydroxide, halide or azide, and R², R³, R⁵, X and nare as defined above. It will be appreciated that when R³ is a protectedpeptide, subsequent N-terminus extension may be carried out usingpeptide synthesis methods known in the art, such as deprotection andfurther peptide bond formation.

The process of the present invention can particularly be used for theproduction of cyclic compounds, for example cyclic peptides.

It will be appreciated that when R³ is C(R^(1′))(R⁹)—N(R¹⁰)(R¹¹), thecompound of formula (II) can be reacted with one or more compounds offormula (V) in a stepwise direction.

The present invention therefore encompasses a compound of formula (VII);

wherein the variables are described above, preferably m is an integer of1 to 50, preferably 1 to 30, more preferably 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20; and R^(1′), R², R⁵, R⁹,R¹⁰, R¹¹, X and n are as defined above.

The compound of formula (VII) can be used in a process for the formationof a compound of formula (I) (illustrated below as (Ic));

when R¹⁴ is —[C(O)—C(R⁹)(R^(1′))—N(R¹⁰)—]_(m)—(R¹¹) and R^(1′), R², R⁶,R⁷, R⁹, R¹⁰, R¹¹, m, X and Y are as described above, comprising,reaction of a compound of formula (VII) with a compound of formula (III)as described above. The compound of formula (I) can then be convertedinto a compound of formula (VI) by removal of the group R⁶ as describedbelow. For the compound of formula (VII) and compounds of formula (I) or(VI) obtained therefrom, the substituents R¹ and R⁹ can be replaced by agroup (═R¹) wherein R¹ is as described above.

It will be appreciated that when m is 3 or more, and R¹⁰ and R¹¹ arehydrogen, condensation can occur at the X—C(O)— functionality of thecompound of formula (VII) to form a cyclised compound of formula (VIII);

wherein the variables are as defined above.

The present invention therefore provides a compound of formula (VIII).In addition, the invention provides a process for the production of acompound of formula (VIII) comprising cyclisation of a compound offormula (VII) wherein m is 3 or more. Reaction of the compound offormula (VIII) under reducing conditions (for example in the presence oflithium and liquid ammonia) results in the formation of a compound offormula (IX);

wherein R^(1′), R², R⁹, X and m are as defined above.

The present invention therefore provides a compound of formula (IX) anda process for the production of a compound of formula (IX) comprisingthe reduction of a compound of formula (VIII).

It will be appreciated that the process of the present invention can becarried out in solution. Alternatively, a compound of formula II may beattached to a resin via the group R⁵ and the peptide synthesis carriedout via solid phase peptide synthesis. When R⁵ is a linker it can be agroup OR¹³, N(R¹³)₂, CO₂R¹³ or SR¹³, or an alkyl group having 1 to 4carbons or a C₆₋₁₂ aryl group, said alkyl and aryl groups beingoptionally substituted with OR¹³, N(R¹³)₂, CO₂R¹³ or SR¹³.Alternatively, part of the synthesis may be carried out on the solidphase and part in solution.

The compound of formula II can be attached to and removed from a resinusing methods known in the art.

Solid phase peptide synthesis using the process of the present inventionmay be carried out by using procedures attaching the carboxy-terminal toany resin known in the art. Examples of suitable resins include Wang,Merrifield, polyamide, 2-chlorotrityl, Rink, Knorr, DCHD, PAL and anyother known in the art. Solid phase coupling partners such as BOP,PyBOP) and DCC may be used, as well as any other suitable couplingpartners known in the art.

A further feature of the first aspect is a process for the production ofa compound of formula (VI)

from formula (I)

by the removal of R⁶ by any method known in the art, wherein X, Y, R²,R³, R⁶ and R⁷ are as defined above. It will be appreciated that when R⁶is hydrogen, the compound of formula (I) corresponds to the compound offormula (VI).

In particular, the removal of the group R⁶ may be carried out underreducing conditions such as under Birch conditions (i.e. with lithiumand liquid ammonia). As it will be appreciated by the skilled person,the peptide produced by the process of the first aspect may be postmodified by any suitable method known in the art. A second aspect of thepresent invention relates to the compounds described herein, including acompound of formula (II)

wherein X is O, S or NR⁸, where R⁸ is C₁₋₆ alkyl C₆₋₁₂ aryl or hydrogenR² is independently selected from a C₁₋₁₀ branched or straight chainalkyl group, C₅₋₁₂ heteroaryl group or C₆₋₁₂ aryl group, optionallysubstituted with OR¹³, SR¹³N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, SO₂R¹², SO₃R¹²phenyl, imidazolyl, indolyl, hydroxyphenyl or NR¹³C(═NR¹³)N(R¹³)₂; R³ isas defined for R² or is hydrogen, or a group

or a group —C(R^(1′))(R⁹)—N(R¹⁰)(R¹¹) wherein R¹ is independentlyselected from a C₁₋₁₀ branched or straight chain alkyl group, C₅₋₁₂heteroaryl group or C₆₋₁₂ aryl group optionally substituted with OR¹³,SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, SO₂R¹², SO₃R¹², phenyl, imidazolyl,indolyl, hydroxyphenyl or NR¹³C(═NR¹³)N(R¹³)₂ wherein when Y is NR⁸, R⁸and R^(1′) can together form a 4 to 7 membered ring, optionallysubstituted with CO₂R¹³, OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, C₁₋₁₀alkyl or C₆₋₁₂ aryl, wherein said ring can be fully, partially orunsaturated,and wherein the ring may contain one or more heteroatoms selected fromO, S or N; R¹² is hydrogen, C₁₋₆ alkyl, C₆₋₁₂ aryl or N(R¹³)₂, whereineach occurrence of R¹³ is independently hydrogen, C₁₋₆ alkyl or C₆₋₁₂aryl, R⁹ and R¹⁰ are independently hydrogen or a group as defined forR¹; or R⁹ and R¹⁰ can together form a 4 to 7 membered ring, optionallysubstituted with CO₂R¹³, OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, C₁₋₁₀alkyl or C₆₋₁₂ aryl, wherein said ring can be fully, partially orunsaturated, and wherein the ring may contain one or more heteroatomsselected from O, S or NR¹¹ is hydrogen or an amino protecting grouppreferably selected from a benzyloxycarbonyl group, a t-butoxycarbonylgroup, a 2-(4-biphenylyl)-isopropoxycarbonyl group, afluorenylmethoxycarbonyl group, a triphenylmethyl group and/or a2-nitrophenylsulphenyl group; R¹ is independently selected from C₁₋₁₀branched or straight chain alkyl optionally substituted with OR¹³, SR¹³,N(R¹³)₂, CO₂R¹³, CO N(R¹³)₂, phenyl, imidazoyl, indolyl, hydroxyphenylor NR¹³C(═NR¹³)N(R¹³)₃ and R^(4′) is a carboxyl protecting group orhydrogen and n is 0, 1, 2 or 3, m is 1-100; and R⁵ is a linker forattachment of formula (II) to a resin, a linked resin, or C₆₋₁₂ aryl,C₅₋₁₂ heteroalkyl or C₁₋₈ branched or straight chain alkyl optionallysubstituted with OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, phenyl,imidazolyl, indolyl, hydroxyphenyl or NR¹³C(═NR¹³)N(R¹³)₂; wherein whenX═O, and R⁵ is phenyl, n is not 0 or 1.

Preferably R¹ and R² are independently selected from C₁₋₄ branched orstraight chain alkyl optionally substituted with OR¹³, SR¹³, N(R¹³)₂,CO₂R¹³, CON(R¹³)₂, phenyl, imidazolyl, indolyl, hydroxyphenyl orNR¹³C(═NR¹³)N(R¹³)₂. More preferably R¹ and R² are independentlyselected from C₁ alkyl optionally substituted with OR¹³, SR¹³, CO₂R¹³,CO N(R¹³)₂, phenyl, imidazolyl, indolyl or hydroxyphenyl; C₂ alkyloptionally substituted with OR¹³, CO₂R¹³, CON(R¹³)₂ or SCH₃; C₃ alkylNR¹³C(═NR¹³)N(R¹³)₂ or C₄ alkyl optionally substituted with N(R¹³)₂.

As set out above, R⁴ is a carboxyl protecting group, such as an estergroup. In particular R⁴ is preferably methyl, ethyl, benzyl, t-butyl orphenyl. When R⁵ is a linker it can be OR¹³, N(R¹³)₂, CO₂R¹³ or SR¹³ oran alkyl group having 1 to 4 carbons or a C₆₋₁₂ aryl group, wherein thealkyl group and/or aryl group can be substituted with one or more ofOR¹³, N(R¹³)₂, CO₂R¹³ or SR¹³.

The integer, m is preferably 1-50, more preferably 1 to 30, mostpreferably 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19 or 20. The integer n is preferably 0 or 1.

When X is NR⁸, R⁸ is preferably C₁₋₄ alkyl, more preferably methyl,ethyl, n-propyl, iso-propyl, n-butyl or tert-butyl, phenyl, naphthyl,anthracenyl or phenanthracenyl, more preferably phenyl or hydrogen.

R¹³ is preferably hydrogen or C₁₋₄ alkyl, more preferably methyl, ethyl,n-propyl, iso-propyl, n-butyl or tert-butyl.

For the purposes of this invention, alkyl relates to both straight chainand branched, saturated or unsaturated alkyl radicals having, forexample, 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms and mostpreferably 1 to 4 carbon atoms including but not limited to methyl,ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyln-pentyl, n-hexyl, n-heptyl, n-octyl. Alkyl therefore relates to a grouphaving 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 or more carbon atoms. The termalkyl also encompasses cycloalkyl radicals of 3 to 12 carbon atoms,preferably 4 to 8 carbon atoms, and most preferably 5 to 6 carbon atomsincluding, but not limited to cyclopropyl, cyclobutyl, CH₂-cyclopropyl,CH₂-cyclobutyl, cyclopentyl or cyclohexyl. Cycloalkyl groups may beoptionally substituted or fused to one or more carbocyclyl orheterocyclyl group. Haloalkyl relates to an alkyl radical preferablyhaving 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms substitutedwith one or more halide atoms for example CH₂CH₂Br, CF₃ or CCl₃. Analkyl group may be optionally interrupted by one or more O, S or NHgroups, preferably one or more O atoms to form an alkoxy group. An alkylgroup may be optionally interrupted by one or more double or triplebonds to form a group including but not limited to ethylene,n-propyl-1-ene, n-propyl-2-ene, isopropylene, ethynyl, 2-methylethynyletc.

“Aryl” means an aromatic 6 to 12 membered hydrocarbon or heteroarylcontaining one ring or being fused to one or more saturated orunsaturated rings including but not limited to phenyl, naphthyl,anthracenyl or phenanthracenyl. “Heteroaryl” means an aromatic 5 to 12membered aryl containing one or more heteroatoms selected from N, O or Sand containing one ring or being fused to one or more saturated orunsaturated rings including but not limited to furan, imidazole, indole,oxazole, purine, pyran, pyridine, pyrimidine, pyrrole, tetrahydrofuran,thiophene and triazole. The aryl and heteroaryl groups can be fullysaturated, partially saturated or unsaturated.

Halogen means F, Cl, Br or I, preferably F.

A third aspect of the invention relates to the use of a compound offormula (II) as defined in the first and/or second aspects of theinvention in asymmetric synthesis.

All preferred features of each of the aspects of the invention apply toall other aspects mutatis mutandis.

The present invention will now be illustrated by reference to one ormore of the following non-limiting examples:

EXAMPLES

Example of a method for the production of a cyclic peptide.

Example of a method for N-terminal extension of a compound of formula(II).

Example of a method for use of the compound of formula (II) in solidphase synthesis

Example of a method to produce a thiomorpholinone template of formula(II)

Examples of Peptide Synthesis(5R)-3-Methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one

(R)-2-phenylglycinol (3.00 g, 21.9 mmol, 1.0 equiv.) and ethyl pyruvate(2.67 mL, 24.1 mmol, 1.1 equiv.) were refluxed in trifluoroethanol (50mL) over activated 4 molecular sieves (8.00 g) for 24 hours. Filtrationthrough a short pad of CELITE® diatomaceous earth and removal of solventfrom the filtrate in vacuo generated the crude product which waspurified by flash column chromatography on silica, eluting with petroland diethyl ether (7:3) to furnish the title compound as a white solid(1.70 g, 41%); mp 71.0-72.0° C. (lit 71.0-72.0° C.); v_((max))(KBr) 3001(C—H), 1734 (C═O), 1642 (C═N) cm⁻¹; δ_(H) (250 MHz, CDCl₃) 7.42-7.32(5H, m, Ph), 4.89-4.80 (1H, m, PhCH), 4.56 (1H, dd, /4.49 Hz, T 11.55Hz, 6β-H), 4.25 (1H, dd, J 10.97 Hz, T 11.51 Hz, 6α-H), 2.40 (3H, s,CH₃); δ_(C) (62.5 MHz, CDCl₃) 160.7, 155.9, 137.2, 129.4, 128.7, 127.5,71.9, 60.1, 22.2; m/z (CL, NH₃), 189 (M⁺, 25%), 159 (12%), 130 (24%),104 (100%), 90 (21%), and 78 (6%); HRMS for C₁₁H₁₁NO₂ requires 189.0787found 189.0782. [α]_(D) ²⁰ −2560.0 (c 1.11 CHCl₃) (lit [α]_(D) ²⁰ −237.1(c 1.11 CHCl₃)).

(3S,5R)-3-Methyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one

To a solution of (5R)-3-methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one(1.70 g, 9.0 mmol, 1.0 equiv.) in anhydrous dichloromethane (60 mL)under an atmosphere of nitrogen was added PtO₂ (170 mg, 0.1 equiv.). Themixture was consecutively degassed and purged three times with hydrogenand then stirred for 5 hours under an atmosphere of hydrogen. Filtrationthrough a short pad of CELITE® diatomaceous earth and removal of solventfrom the filtrate in vacuo yielded the crude product which was purifiedby recrystallisation in dichloromethane, diethyl ether and hexane tofurnish the title compound as white needles (1.37 g, 80%); m.p.82.0-83.0° C. (lit. m.p. 81.0-82.0° C.); v_((max))(KBr) 3314 (N—H), 2981(C—H), 1739 (C═O), cm⁻¹, δ_(H) (250 MHz, CDCl₃) 7.44-7.33 (5H, m, Ph);4.42-4.23 (3H, m, CHCH₂), 3.88 (1H, q, /6.76 Hz, CHCH₃), 1.86 (1H, br,NH), 1.50 (3H, d, J 6.16 Hz, CH₃); δ_(c) (62.5 MHz, CDCl₃) 170.7, 138.0,129.3, 127.5, 127.2, 75.4, 58.2, 55.4, 19.0 m/z (CL, NH₃), 191 (M⁺, 7%),147 (20%), 131 (65%), 104 (100%), 91 (20%), and 77 (12%); HRMS forC₁₁H₁₃NO₂ requires 191.0943 found 191.0940. [α]_(D) ²⁰ −92.9 (c 1.02CHCl₃) (lit. for the enantiomer [α]_(D) ²⁰ +92.3 (c 0.84 CHCl₃)).

(3S,5R)-4-N-Acetyl-3-methyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one

To a vigorously stirred mixture of(3S,5R)-3-methyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (300mg, 1.56 mmol), Na₂CO₃ (500 mg, 4.68 mmol, 3.0 equiv.) in anhydrousdichloromethane (30 mL) was added acetyl chloride (0.17 mL, 2.34 mmol,1.5 equiv.) dropwise over 1 min. The resulting solution was stirred for15 minutes under an atmosphere of nitrogen. The reaction was quenched bythe addition of saturated Na₂CO₃ (20 mL), the aqueous phase wasextracted with diethyl diethyl ether (3×10 mL) and the combined extractswere dried over MgSO₄. The solvents were removed in vacuo and the crudematerial was purified by flash column chromatography on silica, elutingwith diethyl ether and dichloromethane (9:1) to furnish the titlecompound as fine colourless needles (270 mg, 74%); m.p. 82-85° C.;V_((max)) (KBr) 2943 (C—H), 1733 (C═O, lactone), 1647 (C═O, amide)cm^(″1); δ_(H) (250 Mhz, DMSO-d) 7.42-7.36 (5H, m, Ph), 5.49 (0.4H,PhCH×0.4) 5.33 (0.6H, PhCH×0.6), 5.08-5.05 (1H, m, CH₃CH), 4.65 (2H, d,J 6.10 Hz CH₂); 2.13 (1H, s, CH₃CON×1), 1.86 (2H, s, CH₃CON×2), 1.39(3H, d, J 12.40 Hz CH₃CH): δ_(c) (62.5 MHz, DMSO—O 170.5, 169.8, 137.8,129.4, 128.4, 127.1, 68.6, 55.5, 50.7, 49.7, 22.7, 19.0; ^(m)1_(τ) (CL,NH₃), 234 (MH⁺, 8%), 233 (M, 13%), 220 (4%), and 219 (100%); HRMS forC₁₃H₁₆NO₃ requires 234.1126. found 234.1130; [α]_(D) ²⁰ −29.8 (c 1.16CHCl₃).

N-Fmoc-L-alanine acid chloride

To a solution of N-Fmoc-L-alanine (2.00 g, 6.4 mmol, 1.0 equiv.) inanhydrous dichloromethane (40 mL) was added thionyl dichloride (4.70 ml,64 mmol, 10 equiv.). The resulting mixture was refluxed for 2 hoursunder an atmosphere of nitrogen. The solvent and excess of thionylchloride were removed in vacuo and the crude N-Fmoc-L-alanine acidchloride was partially purified by recrystallization fromdichloromethane and hexane (1.74 g, 86%); m.p. 88-90° C. (lit. m.p.112-114° C.); v_((max)) (KBr) 3328 (N—H), 3040 (C—H), 1778 (C═O,chloride), 1694 (C═O, carbamate), cm¹; δ_(H) (250 MHz, CDCl₃) 7.79-7.29(8H, m, Fmoc), 5.22 (1H, d, J 8.0 Hz, NH), 4.67-4.38 (3H, m, CH₃CH×1,CHCH₂×2), 4.23 (1H, t, /6.52 Hz, CHCH₂); 1.55 (3H, d, J 7.28 Hz, CH₃CH);δ_(c) (62.5 MHz, CDCl₃) 176.8, 158.2, 143.9, 141.7, 128.2, 127.5, 125.3,120.5, 67.7, 59.1, 47.5, 17.7; ^(m)1_(z) (CL, NH₃), 330 (MH⁺, 48%), 258(20%), 197 (65%), 154 (100%), 95 (20%), and 72 (12%); HRMS forC₁₈H₁₇ClNO₃ requires 330.1595 found 330.1592. [α]_(D) ²⁰ +8.50 (c 1.30CHCl₃) (lit. [α]_(D) ²⁴ +4.03 (c 1.00 CH₂Cl₂)).

(3S,5R)—N—[N-Fmoc-(S)alanyl]-3-methyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one

To a vigorously stirred mixture of(3S,5R)-3-methyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (600mg, 3.14 mmol). Na₂CO₃ (1.70 g, 15.70 mmol, 5.0 equiv.) in 1:1dichloromethane and water (40 mL) was added N-Fmoc-L-alanine acidchloride (1.26 g, 3.84 mmol, 1.2 equiv.) in dichloromethane (10 mL)dropwise over 5 min. The resulting solution was stirred for 2 hours. Theaqueous phase was extracted with dichloromethane (3×15 mL). The combinedextracts were washed with saturated Na₂CO₃ (50 mL), water (2×30 mL),brine (50 mL) and dried over MgSO₄. The solvents were removed in vacuoand the crude material was purified by flash column chromatography onsilica, eluting with petrol and diethyl ether (1:4) to furnish the titlecompound as fine colorless needles (1.21 g, 80%); m.p. 89-90° C.;V_((max)) (KBr) 3321 (N—H)₅ 2983 (C—H), 1741 (C═O, lactone), 1718 (C═O,carbamate), 1654 (C═O, amide) cm^(″1); δ_(H) (250 MHz, DMSO-d) 7.91-7.27(13H, m, Fmoc×8, Ph×5), 5.50 (1H, br, NH), 5.07 (1H, m, PhCH), 4.90 (1H,m, NCHCH₃); 4.77 (1H, d, 77.0 Hz, Cc-PhCHCH₂), 4.57 (2H, m, CHCH₃NH×1,β-PhCHCH₂×1), 4.26 (1H, m, OCH₂CH), 4.19 (2H, m, OCH₂CH), 1.28 (3H, d,/4.O Hz₅ NCHCH₃), 1.10 (3H, d, /4.0 Hz, CHCH₃NH); δ_(c) (62.5 MHz,OMSO-d) 172.0, 170.0, 156.1, 144.2, 141.1, 136.2, 128.9, 128.3, 127.9,127.4, 126.7, 125.7, 120.4, 66.0, 65.3, 53.0, 50.7, 47.8, 46.9, 18.6,17.8; ^(m)1_(z) (Cl, NH₃), 508 (MNa⁺, 6%), 502 (MNH₄ ⁺, 45%), 487 (4%),and 485 (MH⁺, 100%); HRMS for C₂₉H₂₉N₂O₅ requires 485.2069. found485.2060; [α]_(D) ²⁰ −13.1 (c1.06 CHCl₃).

(5S)-3-Methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one

(S)-2-phenylglycinol (3.00 g, 21.9 mmol, 1.0 equiv.) and ethyl pyruvate(2.67 mL, 24.1 mmol, 1.1 equiv.) were refluxed in trifluoroethanol (50mL) over activated 4 molecular sieves (8.00 g) for 24 hours. Filtrationthrough a short pad of CELITE® diatomaceous earth and removal of solventfrom the filtrate in vacuo generated the crude product which waspurified by flash column chromatography on silica, eluting with petroland diethyl ether (7:3) to furnish the title compound as a white solid(1.83 g, 44%); m.p. 70.0-71.0° C. (lit 71.0-72.0° C.); v_((max))(KBr)3007 (C—H), 1735 (C═O), 1640 (C═N) cm⁻¹; δ_(H), (250 MHz, CDCl₃)7.45-7.32 (5H, m, Ph), 4.88-4.81 (1H, m, PhCH), 4.56 (1H, dd, J 4.49 Hz,T 9.48 Hz, 6β-H), 4.25 (1H, dd/13.01 Hz, JT 14.99 Hz, 6α-H), 2.41 (3H,s, CH₃); δ_(c) (62.5 MHz CDCl₃) 160.7, 155.9, 137.2, 129.4, 128.7,127.5, 71.9, 60.1, 22.2; m/z (CL, NH₃), 189 (M⁺, 25%), 159 (12%), 130(24%), 104 (100%), 90 (21%), and 78 (6%); HRMS for C₁₁H_(n)NO₂ requires189.0787 found 189.0782. [α]_(D) ²⁰ +253.0 (c 0.98 CHCl₃) (theenantiomer lit. [α]_(D) ²⁰ −237.1 (c 1.11 CHCl₃)).

(3S)-3-Methyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one

To a solution of (5S)-3-methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one(1.70 g, 9.0 mmol, 1.0 equiv.) in anhydrous dichloromethane (60 mL)under an atmosphere of nitrogen was added PtO₂ (170 mg, 0.1 equiv.). Themixture was consecutively degassed and purged three times with hydrogenand then stirred for 5 hours under an atmosphere of hydrogen. Filtrationthrough a short pad of CELITE® diatomaceous earth and removal of solventfrom the filtrate in vacuo yielded the crude product which was purifiedby recrystallisation in dichloromethane, diethyl ether and hexane tofurnish the title compound as white needles (1.26 g, 74%); m.p.81.0-82.0° C. (lit. m.p. 81.0-82.0° C.); v_((max))(KBr) 3314 (N—H), 2981(C—H), 1736 (C═O), cm⁻¹; δ_(H) (250 MHz, CDCl₃) 7.43-7.26 (5H, m, Ph);4.42-4.23 (3H, m, CHCl₂), 3.88 (1H, q, /6.76 Hz, CHCH₃), 1.80 (1H, br,NH), 1.50 (3H, d, J 6.76 Hz, CH₃); δ_(c) (62.5 MHz, CDCl₃) 170.7, 138.1,129.3, 129.1, 127.5, 75.4, 58.2, 55.4, 19.0; m/z (CL, NH₃), 192 (MH⁺,30%), 147 (68%), 132 (64%), 104 (100%), and 91 (10%); HRMS for C₁₁H₁₃NO₂requires 192.1025 found 192.1019. [α]_(D) ²⁰ +88.8 (c 0.96 CHCl₃) (lit.[α]_(D) ²⁰ +92.3 (c 0.84 CHCl₃)).

(3R,5S)—N—[N-Fmoc(S)alanyl]-3-methyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one

To a vigorously stirred mixture of(3R,5S)-3-methyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (500mg, 2.62 mmol), Na₂CO₃ (1.40 g, 13.3 mmol, 5.0 equiv.) in 1:1dichloromethane and water (40 mL) was added N-Fmoc-L-alanine acidchloride (1.04 g, 3.14 mmol, 1.2 equiv.) in dichloromethane (10 mL)dropwise over 5 min. The resulting solution was stirred for 2 hours. Theaqueous phase was extracted with dichloromethane (3×15 mL). The combinedextracts were washed with saturated Na₂CO₃ (50 mL), water (2×30 mL),brine (50 mL) and dried over MgSO₄. The solvents were removed in vacuoand the crude material was purified by flash column chromatography onsilica, eluting with petrol and diethyl ether (1:4) to furnish the titlecompound as fine colourless needles (1.02 g, 80%); m.p. 87-88° C.;v_((max))(KBr) 3323 (N—H), 2982 (C—H), 1761 (C═O, lactone), 1717 (C═O,carbamate), 1656 (C═O, amide) cm^(″1); δ_(H) (400 MHz. DMSO-d, 110° C.)7.84-7.29 (13H, m, Fmoc×8, Ph×5), 7.08 (1H, br, NH), 5.54 (1H, t, /5.88Hz, PhCH), 4.96 (1H, q, /7.11 Hz NCHCH₃); 4.68-4.60 (2H, m, PhCHCH₂),4.41-4.32 (3H, m, CHCH₃NH×1, OCH₂CH×2), 4.22 (1H, t, /6.72 Hz OCH₂CH),1.45 (3H, d, /7.15 Hz, NCHCH₃), 1.08 (3H, d, /6.71 Hz, CHCH₃NH); δ_(c)(62.5 MHz, OMSO-d) 174.0, 172.8, 170.4, 169.6, 156.3, 144.1, 141.1,137.7, 129.4, 128.7, 128.0, 127.4, 127.3, 127.1, 125.6, 120.5, 68.8,66.0, 55.5, 55.3, 52.2, 51.4, 50.0, 47.2, 20.5, 18.6, 17.7, 17.1;^(m)1_(z) (C.I. NH₃), 485 (MH⁺, 12%), 431 (8%), 381 (7%), 281 (15%) and149 (100%); HRMS for C₂₉H₂₉N₂O₅ requires 485.2069. found 485.2076;[α]_(D) ²⁰ +22.2 (c 0.94 CHCl₃).

(5R)-3-Isopropyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one

(R)-2-phenylglycinol (4) (2.00 g, 14.6 mmol, 1.0 equiv.) and ethyl3-methyl-2-oxobutyrate (2.20 mL, 14.6 mmol. 1.0 equiv.) were refluxed intrifluoroethanol (30 mL) over activated 4 molecular sieves (7.0 g) for24 hours. Filtration through a short pad of CELITE® diatomaceous earthand removal of solvent from the filtrate in vacuo generated the crudeproduct which was purified by flash column chromatography on silica,eluting with petrol and diethyl ether (4:1) to furnish the titlecompound as a colourless oil (1.13 g, 36%); v_((max))(film) 2965 (C—H),1740 (C═O), 1638 (C═N) cm⁻¹; δ_(H) (250 MHz, CDCl₃) 7.45-7.32 (5H, m,Ph), 4.90-4.83 (1H, m, PhCH), 4.55 (1H, dd, J 4.4 Hz, T 11.5 Hz, 6β-H),4.13 (1H, dd/10.9 Hz, T 11.4 Hz, 6α-H), 3.32 (1H, m, CH(CH₃)₂), 1.25(3H, d, J 5.0 Hz, CH(CH₃)₂×3), 1.22 (3H, d, /5.0 Hz, CH(CH₃)₂×3); δ_(c)(62.5 MHz, CDCl₃) 167.7, 155.7, 137.5, 129.3, 128.6, 127.4, 71.7, 59.7,32.7, 20.7, 19.9: m/z (CL, NH₃), 220 (100%), 218 (MH⁺, 17%), 217 (27%),and 216 (25%); HRMS for C₁₃H₁₆NO₂ requires 218.1177 found 218.1181.[α]_(D) ²⁰ −207.5 (c 1.17 CHCl₃).

(3S,5R)-3-Isopropyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (39)

To a solution of(5R)-3-isopropyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one (38) (1.03 g,4.74 mmol, 1.0 equiv.) in anhydrous dichloromethane (50 mL) under anatmosphere of nitrogen was added PtO₂ (103 mg, 0.1 equiv.). The mixturewas consecutively degassed and purged three times with hydrogen and thenstirred for 5 hours under an atmosphere of hydrogen. Filtration througha short pad of CELITE® diatomaceous earth and removal of solvent fromthe filtrate in vacuo yielded the crude product which was purified byflash column chromatography on silica eluting with petrol and diethylether (4:1) to furnish the title product as a waxy solid (662 mg, 64%);m.p. 61.5-62.5° C.; v_((max))(KBr) 3326 (N—H—), 2960 (C—H), 1733 (C═O),cm⁻¹; δ_(H) (250 MHz, CDCl₃) 7.47-7.35 (5H, m, Ph); 4.33-4.18 (3H, m,PhCHCH₂), 3.81 (1H, m, NHCH), 2.49, (1H, m, CH(CH₃)₂), 1.68 (1H, br,NH), 1.09 (3H, dd, J 6.75 Hz, CH(CH₃)₂×3), 1.05 (3H, dd, J 6.75,CH(CH₃)₂×3); δ_(C), (62.5 MHz, CDCl₃) 170.3, 138.5, 129.3, 129.1, 127.6,74.9, 64.2, 57.3, 32.0, 19.4, 17.4; m/z (Cl, NH₃), 237 (MNH₄ ⁺, 5%), 220(100%, MH⁺), 219 (22%), and 216 (6%); HRMS for C₁₃H₁₈NO₂ requires220.1333 found 220.1338. [α]_(D) ²⁰ −92.1 (c 1.45 CHCl₃).

(3S,5R)—N—[N-Fmoc-(S)alanyl]-3-isopropyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one

Method 1:

To a solution of(3S,5R)-3-isopropyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (150mg, 0.68 mmol) in anhydrous dichloromethane (10 mL) was addedN-Fmoc-L-alanine acid chloride (276 mg, 0.82 mmol, 1.2 equiv.) inanhydrous dichloromethane (5 mL). The resulting solution was stirred for24 hours. The solvent was removed in vacuo and the crude material waspurified by flash column chromatography on silica, eluting with petroland diethyl ether (2:3) to furnish the title product as colourless fineneedles (95 mg, 27%).

Method 2:

To a vigorously stirred solution of(3S,5R)-3-isopropyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (200mg, 0.91 mmol) and Na₂CO₃ (415 mg, 2.73 mmol, 3.0 equiv.) in anhydrousdichloromethane (15 mL) was added N-Fmoc-L-alanine acid chloride (428mg, 1.36 mmol, 1.5 equiv.) in anhydrous dichloromethane (10 mL). Theresulting mixture was stirred under nitrogen for 1 hour. Filtrationthrough a short pad of CELITE® diatomaceous earth and removal of solventfrom the filtrate in vacuo furnished the crude material which waspurified by flash column chromatography on silica, eluting with petroland diethyl ether (3:7) to furnish the title product as colourless fineneedles (380 mg, 82%); m.p. 72-75° C.; v_((max))(KBr) 3402 (N—H), 2969(C—H), 1760 (C═O, lactone), 1718 (C═O, carbamate), 1654 (C═O, amide)cm⁻¹; δ_(H) (250 MHz, CDCl₃) 7.65-7.15 (13H, m, Fmoc×8, Ph×5), 5.46 (1H,br, NH), 5.03-4.98 (1H, m, PhCH), 4.75 (1H, d, /10.0 Hz CHCH(CH₃)₂),4.32-4.13 (3H, m, PhCHCH₂ and OCH₂CH), 4.07-4.02 (1H, m, CHCH₃),3.89-3.79 (2H, m, OCH₂CH), 2.18-2.00 (1H, m, CH(CH₃)₂), 1.21 (3H, d, J5.5 Hz, CH(CH₃)₂×3), 1.19 (3-H, d, /5.0 Hz, CHCH₃), 1.02 (3H, d, J 6.5Hz, CH(CH₃)₂×3); δ_(c) (62.5 MHz, CDCl₃) 174.1, 167.1, 153.7, 142.8,140.2, 134.9, 128.8, 128.2, 127.2, 124.9, 124.1, 118.9, 66.3, 65.7,55.2, 52.5, 47.5, 45.0, 31.6, 20.1, 18.2, 17.8; m/z (Cl, NH₃), 535(MNa⁺, 73%), 513 (MH⁺, 100%), 334 (11%), 333 (53%), 328 (23%), and 311(19%); (Cl.) HRMS for C₃₁H₃₃N₂O₅ requires 513.2381. found 513.2378.[α]_(D) ²⁰ −22.1 (c 1.05 CHCl₃).

N-Fmoc-L-valine acid chloride

To a solution of N-Fmoc-L-alanine (3.00 g, 8.7 mmol, 1.0 equiv.) inanhydrous dichloromethane (40 mL) was added thionyl chloride (6.5 mL, 87mmol, 10.0 equiv.). The resulting mixture was refluxed for 2 hours underan atmosphere of nitrogen. The solvent and excess of thionyl dichloridewere removed in vacuo and the crude N-Fmoc-L-alanine acid chloride waspartially purified by recrystallization from dichloromethane and hexane(2.50 g, 80%); m.p. 75-79° C. (lit. m.p. 111-112° C.); v_((max)) (KBr)3317 (N—H), 2969 (C—H), 1788 (C═O, acid chloride), 1696 (C═O,carbamate), cm^(″1); δ_(H) (250 MHz, CDCl₃) 7.78-7.29 (8H, m, Fmoc),5.20 (1H, d, J 9.5 Hz, NH), 4.55-4.33 (3H, m, CH₃CH×1, CHCH₂×2), 4.23(1H, t, J 6.5 Hz, CHCH₂); 2.40 (1H, m, CH(CH₃)₂), 1.05 (3H, d, J 7.0 Hz,CH(CHg)₂×3), 0.95 (3H, d, /7.0 Hz, CH(CHb)₂×3); δ_(c) (62.5 MHz, CDCl₃)175.4, 157.1, 143.9, 141.8, 128.2, 127.5, 125.3, 120.5, 68.2, 67.7,47.5, 30.3 19.7, 17.4; [α]_(D) ²⁰ +13.2 (c 1.05 CHCl₃) (lit. [α]_(D) ²⁴+5.5 (c 1.00 CH₂Cl₂)).

(3S,5R)—N—[N-Fmoc-(S)valinyl]-3-isopropyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one

Method 1:

To a solution of(3S,5R)-3-wøpropyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (200mg, 0.91 mmol) in anhydrous dichloromethane (20 mL) was addedN-Fmoc-L-valine acid chloride (391 mg, 1.10 mmol, 1.2 equiv.) inanhydrous dichloromethane (5 mL). The resulting solution was stirred for24 hours. The solvent was removed in vacuo and the crude material waspurified by flash column chromatography on silica, eluting with petroland diethyl ether (2:3) to furnish the title product as colourless fineneedles (80 mg, 16%).

Method 2:

To a vigorously stirred solution of(3S,5R)-3-isopropyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (200mg, 0.91 mmol) and Na₂CO₃ (415 mg, 2.73 mmol, 3.0 equiv.) in anhydrousdichloromethane (15 mL) was added N-Fmoc-L-valine acid chloride (533 mg,1.36 mmol, 1.5 equiv.) in anhydrous dichloromethane (10 mL). Theresulting mixture was stirred under nitrogen for 6 hours. Filtrationthrough a short pad of CELITE® diatomaceous earth and removal of solventfrom the filtrate in vacuo furnished the crude material which waspurified by flash column chromatography on silica, eluting with petroland diethyl ether (1:1) to furnish the title product as colourless fineneedles (260 mg, 52%); m.p. 75-78° C.; V_((max))(KBr) 3421 (N—H), 2966(C—H), 1763 (C═O, lactone), 1718 (C═O, carbamate), 1654 (C═O, amide)cm⁻¹; δ_(H) (400 MHz, DMSO-d₆, 120° C.) 7.83-7.25 (13H, m, Fmoc×8,Ph×5), 6.81 (1H, br, NH), 5.34 (1H, dd, /6.2 Hz, /10.8 Hz, PhCH), 4.77(1H, d, /9.5 Hz, NCH), 4.58 (1H, dd, J 6.2 Hz, /12.5 Hz, PhCHCH₂×1),4.47 (1H, dd, J 10.8 Hz, J 12.4 Hz, PhCHCH₂×1), 4.32-4.28 (1H, m,CH₃CH), 4.24-4.15 (3H, m, OCH₂Cl), 2.22-2.05 (2H, m, CH—(CH₃)₂×2), 1.18(3H, d, J 6.5 Hz, CH(CH₃)₂×3), 0.96 (3H, d, J 6.5 Hz, CHCH₃), 0.84 (6H,t, J 7.0 Hz, CH(CH₃)₂×6); δ_(c) (62.5 MHz, CDCl₃) 174.5, 168.5, 155.5,144.2, 141.7, 130.2, 129.6, 128.1, 127.4, 126.7, 126.4, 125.5, 120.4,68.0, 67.1, 61.3, 57.7, 57.0, 47.4, 33.2, 32.6, 21.8, 20.1, 19.7, 18.4,17.5; m/z (CL), 614 (100%), 576 (50%), 564 (9%), 541 (MH⁺), 519 (22%),and 503 (16%); HRMS for C₃₃H₃₇N₂O₅ requires 541.2692 found 541.2709.[α]_(D) ²⁰ −28.5 (c 0.56 CHCl₃).

Phenacyl N-tert-butoxycarboxyl-(S)-phenylalanate

To a solution of potassium hydroxide (0.64 g, 11.31 mmol) in methanol(15 mL) was added Boc-L-phenylalanine (3.00 g, 11.31 mmol). Theresulting solution was stirred at room temperature for 3 hours. Thesolvent was removed and the crude material was dried in vacuo to yieldwhite powder which was subsequently added in anhydrousN,N-dimethylformamide (15 mL) and treated with 2-bromoacetophenone (2.07g, 13.57 mmol, 1.2 equiv.). The resulting solution was stirred at roomtemperature under nitrogen for 24 hours and was quenched by addition ofwater (20 mL). The precipitate can be either used as crude in next stepor purified by recrystallization from diethyl ether yield the titlecompound as white fine needles (3.55 g, 82%); mp 140.0-141.0° C.;V_((max)) (KBr) 3395 (N—H), 2973 (C—H), 1757 (C═O, ester), 1715 (C═O,ketone), 1692 (C═O, carbamate) cm^(″1): δ_(H) (250 MHz CDCl₃) 7.93-7.24(10H, m, Ph), 5.50 (1H, d, /16.4 Hz, OCH₂×1), 5.31 (1H, d, /16.4 Hz,OCH₂×1), 4.97 (1H, d, J 18.1 Hz, NH), 4.75 (1H, dd, /7.2 Hz, r 6.1 Hz,CH), 3.36 (1H, dd, /5.4 Hz, r 14.1 Hz, PhCH₂×1), 3.14 (1H, dd, /7.1 Hz,/^(v) 14.0 Hz, PhCH₂×1), 1.40 (9H, s, f-butyl); δ_(c) (62.5 MHz, CDCl₃)191.9 172.0, 155.6, 136.5, 134.4, 129.9, 129.3, 129.0, 128.2, 127.4,80.4, 66.8, 54.7, 38.6, 28.7. [α]_(D) ²⁰ −7.9 (c 1.01 CHCl₃).

(3S)-3-Benzyl-5-phenyl-3,6-dihydro-2H-1,4-oxazin-2-one

To a suspension of phenacyl N-tert-butoxycarboxyl-(S)-phenylalanate(3.51 g, 9.16 mmol) in diethyl ether (150 mL) was added hydrogen bromidein acetic acid (33% w/w, 4.8 mL, 27.5 mmol, 3.0 equiv.). The resultingmixture was stirred under nitrogen for 3 hours during which time anotherportion of diethyl ether (100 mL) was added. The solid was separated byfiltration through a sinter, washed with diethyl ether (2×30 ml) anddried in vacuo to furnish the amino ester hydrobromide which wassubsequently dissolved in pH 5 acetate buffer (100 mL, 0.2 M, preparedfrom 70 parts 0.2 M aqueous sodium acetate and 30 parts 0.2 M aqueousacetic acid). The resulting mixture was stirred under nitrogen for 12hours during which time yellow oil was formed. The precipitate can beeither used as crude in next step or purified by flash columnchromatography on silica, eluting with petrol and diethyl ether (3:2) tofurnish the title compound as white solid (1.56 g, 65%); v_((max)) (KBr)2932 (C—H), 1751 (C═O), cm^(″1); m.p. 57.0-59.0° C. (lit. 58.0-60.0°C.)⁶³; δ_(H) (250 MHz, CDCl₃) 7.90-7.18 (1OH, m, Ph), 5.01 (1H, d, /14.2Hz, CHCH₂O×1), 4.83 (H, m, CHCH₂Ph), 4.06 (1H, m, CHCH₂), 4.11 (1H, d, J14.2 Hz, CHCH₂O×1), 3.46 (1H, dd, /5.45 Hz, /13.5 Hz, CHCH₂Ph×1), 3.32(1H, dd, /5.45 Hz, /13.5 Hz, CHCH₂Ph×1); δ_(c) (62.5 MHz, CDCl₃) 169.0,162.8, 136.6, 134.7, 131.7, 130.6, 129.2, 128.8, 127.6, 126.3, 67.8,61.0, 39.4; % (CL, NH₃), 266 (32%), 265 (M⁺, 100%), 264 (42%), 263 (5%)and 262 (3%); HRMS for C₁₇H₁₅NO₂ requires 265.1103. found 265.1108.[α]_(D) ²⁰ +85.1 (c 1.04 CHCl₃) (lit. [α]_(D) ²⁰ +85.7 (c 2.00 CHCl₃)).

(3S,5R)-3-benzyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one

To a solution of (3S)-3-Benzyl-5-phenyl-3,6-dihydro-2H-1,4-oxazin-2-one(1.56 g, 5.88 mmol, 1.0 equiv.) in anhydrous methanol (40 mL) under anatmosphere of nitrogen was added palladium on activated carbon (156 mg,0.1 equiv. by mass). The mixture was consecutively degassed and purgedthree times with hydrogen and then stirred for 5 hours under anatmosphere of hydrogen. Filtration through a short pad of CELITE®diatomaceous earth and removal of solvent from the filtrate in vacuoyielded the crude product which was purified by flash columnchromatography on silica eluting with petrol and diethyl ether (4:1) tofurnish the title product as a white solid (514 mg, 33%); m.p.75.0-76.0° C. (lit. 76.0-78.0° C.); v_((max))(KBr) 3321 (N—H), 2949(C—H), 1731 (C═O), cm⁻¹; δ_(H) (250 MHz, CDCl₃) 7.36-7.21 (10H, m, Ph),4.34-4.15 (3H, m, PhCHCH₂), 3.97 (1H, dd, J 3.2, T 10.0 Hz, NHCH), 3.56,(1H, dd, J 3.2, J 13.6 Hz, CHPh×1), 3.00, (1H, dd, /10.0, T 13.6 Hz,CH₂Ph×1), 1.84 (1H, br, NH); δ_(H), (62.5 MHz, CDCl₃) 169.6, 138.0,137.8, 129.8, 129.3, 129.2, 129.1, 127.5, 127.4, 75.3, 60.6, 57.9, 39.4;m/z (CL, NH₃), 268 (MH⁺, 40%), 267 (80%, M⁺), 223 (100%), and 209 (57%);HRMS for C₁₇H₁₇NO₂ requires 267.1259 found 267.1263. [α]_(D) ²⁰ −156.4(c 1.02 CHCl₃) (lit. [α]_(D) ²⁰ −157.9 (c 2.00 CHCl₃)).

(3S,5R)—N—[N-Fmoc-(S)-alanyl]-3-benzyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one

To a vigorously stirred solution of(3S,5R)-3-benzyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (200mg, 0.75 mmol) and Na₂CO₃ (239 mg, 2.25 mmol, 3.0 equiv.) in anhydrousdichloromethane (20 mL) was added N-Fmoc-L-alanine acid chloride (354mg, 1.12 mmol, 1.5 equiv.) in anhydrous dichloromethane (6 mL). Theresulting mixture was stirred under nitrogen for 4 hours. Filtrationthrough a short pad of CELITE® diatomaceous earth and removal of solventfrom the filtrate in vacuo furnished the crude product which waspurified by flash column chromatography on silica, eluting with petroland diethyl ether (2:3) to furnish the title product as colourless fineneedles (150 mg, 36%); m.p. 87-89° C.; v_((max))(KBr) 3413 (N—H), 2981(C—H), 1760 (C═O, lactone), 1718 (C═O, carbamate), 1656 (C═O, amide)cm⁻¹; δ_(H) (400 MHz, DMSO-d, 100° C.) 7.90-7.27 (18H, m, Fmoc×8,Ph×10), 7.07 (1H, br, NH), 5.47 (1H, dd, /4.8 Hz, /7.6 Hz, PhCH), 5.32(1H, t, J 7.2 Hz, NCH), 4.82 (1H, dd, /7.6 Hz, J 12.4 Hz, PhCHCH₂×1),4.71 (1H, dd, J 12 Hz, J′ 12.4 Hz, PhCHCH₂×1), 4.41 (1H, q, J 6.4 Hz,CH₃CH), 4.37-4.21 (3H, m, OCH₂CH), 3.15 (2H, d, /6.8 Hz, CH₂Ph), 1.21(3H, d, /6.8 Hz, CH₃); δ_(c) (62.5 MHz, CDCl₃) 174.8, 170.8, 168.8,159.6, 155.0, 142.7, 140.2, 128.9, 128.5, 127.9, 127.6, 127.4, 126.9,126.6, 126.1, 124.2, 119.0, 66.2, 62.1, 61.0, 52.5, 47.8, 45.9, 33.8,15.6; m/z (CL), 560 (M⁺), 502 (100%), 464 (43%), 426 (19%), and 414(83%); HRMS for C₃₅H₃₂N₂O₅ requires 560.2303 found 560.2293. [α]_(D) ²⁰−56.2 (c 1.01 CHCl₃).

(3S,5R)—N—[N-Fmoc-(S)-alanyl]-3-tert-butyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one

To a vigorously stirred solution of(3S,5R)-3-tert-butyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one(150 mg, 0.63 mmol) in anhydrous dichloromethane (15 mL) and Na₂CO₃ (341mg, 3.22 mmol, 5.0 equiv.) was added N-Fmoc-L-alanine acid chloride (298mg, 0.95 mmol, 1.5 equiv.). The resulting mixture was stirred under anatmosphere of nitrogen for 18 hours. Filtration through a short pad ofCELITE® diatomaceous earth and removal of solvent from the filtrate invacuo gave the crude material which was purified by flash columnchromatography on silica, eluting with petrol and diethyl ether (1:1) tofurnish the title product as colourless fine needles (170 mg, 51%); m.p.74-75° C.; v_((max))(KBr) 2976 (C—H), 1752 (C═O, lactone), 1724 (C═O,carbamate), 1662 (C═O, amide) cm⁻¹; δ_(H) (250 MHz, DMSO-d₆) 7.90-7.29(13H, m, Fmoc×8, Ph×5), 5.39 (1H, br, PhCH), 4.62 (2H, br, CH₂O), 4.33(1H, br, CH₃CH), 4.18 (3H, br, OCH₂CH), 1.23 (3H, d, /6.70 Hz, CHCH₃),0.88 (9H, s, OCH); δ_(c), (62.5 MHz, DMSO-d₆) 175.9, 168.1, 155.8,144.2, 144.1, 141.0, 137.1, 129.0, 128.0, 127.4, 125.8, 125.7, 120.4,66.0, 62.2, 55.3, 53.0, 48.7, 46.9, 37.0, 28.6, 17.4; m/z (CL): 528(15%), 527 (MB⁺, 34%), 526 (M, 100%), 470 (62%), and 414 (74%); HRMS forC₃₂H₃₄N₂O₅ requires 526.459 found 526.2457. [α]_(D) ²⁰ −10.9 (c 1.20CHCl₃).

(3S,5R)—N—[N-Fmoc-(S)valinyl]-3-tert-butyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one

To a vigorously stirred solution of(3S,5R)-3-tert-butyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (75mg, 0.32 mmol) in anhydrous dichloromethane (7 mL) and Na₂CO₃ (170 mg,1.61 mmol, 5.0 equiv.) was added N-Fmoc-L-valine acid chloride (170 mg,0.48 mmol, 1.5 equiv.). The resulting mixture was stirred under anatmosphere of nitrogen for 48 hours. Filtration through a short pad ofCELITE® diatomaceous earth and removal of solvent from the filtrate invacuo gave the crude material which was purified by flash columnchromatography on silica, eluting with petrol and diethyl ether (1:1) tofurnish the title product as colourless fine needles (32 mg, 18%); m.p.71-73° C.; v_((max))(KBr) 2964 (C—H), 1752 (C═O, lactone), 1734 (C═O,carbamate), 1655 (C═O, amide) cm⁻¹; δ_(H) (250 MHz, CDCl₃) 7.77-7.25(13H, m, Fmoc×8, Ph×5), 5.30 (1H, br, (CH₃)₂CHCH), 5.13 (1H, t, J 10.0Hz, PhCH), 4.52-4.38 (2H, m, PhCHCH₂O), 4.29-4.21 (1H, n, OCH₂CH), 4.15(3H, br, OCH₂CH×2 and CHC(CH₃)₃), 1.99-1.96 (1H, m, (CH₃)₂CH), 1.22 (9H,s, C(CH₃)₃); 0.97-0.84 (6H, m, (CH₃)₂CH); δ_(c) (62.5 MHz, CDCl₃) 175.9,168.4, 155.4, 144.2, 141.7, 136.5, 130.2, 129.2, 128.1, 127.6, 126.4,125.5, 120.4, 68.3, 67.1, 64.3, 57.6, 56.5, 47.5, 38.0, 32.7, 30.7,20.2, 17.4; m/z (CL), 554 (MH⁺, 14%), 502 (100%), 464 (40%), 426 (20%),and 414 (74%); HRMS for C₃₄H₃₈N₂O₅ requires 554.2781 found 554.2790.[α]_(D) ²⁰ −17.5 (c 1.48 CHCl₃).

N-t-Boc-(S)-alanyl-N-(1-phenyl-2-hydroxylethyl)glycyl-(S)-alaninetert-butyl ester

To a suspension of L-alanine t-butyl ester hydrochloride (408 mg, 2.3mmol) and(5S)-4-[N-?-Boc-(S)-alanyl]-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one(0.78 g, 2.3 mmol) in anhydrous dioxane (20 mL) was added distilledtriethylamine (0.32 mL, 2.3 mmol). The resulting mixture was stirred atroom temperature vigorously for 5 days. Water (20 mL) was added and themixture was extracted with diethyl ether (3×25 mL). The combined organicextracts were washed with brine (50 mL) and dried over MgSO₄. Thesolvents were removed in vacuo and the crude product was purified byflash column chromatography on silica, eluting with petrol, diethylether, and methanol (10:10:1) to furnish the title compound as finecolourless needles (0.67 g, 59%); mp 69.0-70.0° C.; v_((max)) (KBr) 3312(O—H), 2980 (C—H), 1738 (C═O, lactone), 1701 (C═O, carbamate), 1654(C═O, amide) cm^(″1); δ_(H) (250 MHz, DMSO—O 8.69 (1H, d, J 7.0 Hz, NH),7.39 (1H, d, J 7.0 Hz, NH), 7.40-7.26 (5H, m, Ph), 5.80-5.74 (1H, m,PhCH), 5.07-5.02 (1H, m, OH), 4.69 (1H, d, J 14.0 Hz, NCH₂×1), 4.13-4.04(2H, m, CH₃CH×2), 3.96-3.91 (1H, m, HOCH₂), 3.77-3.74 (1H, m, HOCH₂),3.63 (1H, d, 18.0 Hz, NCH₂×1), 1.43 (18H, s, f-butyl×2), 1.23 (3H, d, J13.0 Hz, CH₃), 1.12 (3H, d, J 13.0 Hz₅CH₃); δ_(c) (62.5 MHz, DMSO-J)176.2, 172.0, 170.7, 156.1, 138.3, 129.0, 128.5, 127.5, 80.9, 78.6,60.2, 57.5, 49.0, 46.7, 28.5, 27.9, 17.4, 16.9: % (CL, NH₃), 494 (MH⁺,8%), 476 (6%), 376 (35%), 293 (21%), 249 (46%), and 44 (100%); HRMS forC₂₅H₄₀N₃O₇ requires 494.2856. found 494.2872. [α]_(D) ²⁰ +24.3 (c 1.09CHCl₃).

L-Alanine tert-butyl ester

To a mixture of sodium carbonate (875 mg, 8.25 mmol, 5.0 equiv.) indeioned water (10 mL) and diethyl ether (10 mL) was added L-alaninetert-butyl ester hydrochloride (300 mg, 1.65 mmol, 1.0 equiv.). Theresulting solution was stirred under an atmosphere of nitrogen for 1hour. The aqueous phase was extracted with diethyl ether (3×10 mL) andthe combined extracts were dried over MgSO₄. The solvent was removed invacuo to settle the title compounds as a colourless oil (200 mg, 84%);v_((max)) (film) 3377 (N—H), 2978 (C—H), 1729 (C═O) cm^(″1); δ_(H) (250MHz, CDCl₃) 3.42 (1H, q, J 7.02 Hz CH), 1.63 (2H, br, NH₂), 1.46 (9H, s,(CH₃)₃), 1.29 (3H, d, J 7.02 Hz, CH₃CH); δ_(c) (62.5 MHz, CDCl₃) 177.1,81.2, 51.0, 28.4, 21.2; [α]_(D) ²⁰ +3.7 (c 0.97 CHCl₃), (lit. [α]_(D) ²⁴+2.3 (c 1.00 CHCl₃)).

N-Fmoc-(S)-alanyl-N-((1R)-phenyl-2-hydroxylethyl)-(S)-alanyl-(S)-alaninetert-butyl ester

Method 1:

(3S,5R)—N—[N-Fmoc-(S)alanyl]-3-methyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one(300 mg, 0.62 mmol) and L-alanine tert-butyl ester (135 mg, 0.93 mmol,1.5 equiv.) were dissolved in anhydrous dichloromethane (14 mL) in adoubly sealed PTFE cylinder and subjected to ultra-high pressure of 19kbar for 48 hours. After releasing the pressure, the solution wasfiltered through a short pad of CELITE® diatomaceous earth and removalof solvent from the filtrate in vacuo yielded the crude product whichwas purified by flash column chromatography on silica, eluting withdiethyl ether and dichloromethane (4:1) to furnish the starting material(33) (40 mg, 133%) and the title product as fine colourless needles (122mg, 31%).

Method 2:

To a solution of L-alanine tert-butyl ester (466 mg (466 mg, 3.21 mmol,3.0 equvi.) in anhydrous dichloromethane (30 mL) was added trimethylaluminium (1.87 mL, 3.75 mmol, 2 M in hexane, 3.5 equiv.) under anatmosphere of nitrogen. After 15 minutes,(3S,5R)—N—[N-Fmoc-(S)alanyl]-3-methyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one(520 mg, 1.07 mmol) in anhydrous dichloromethane (10 mL) was added. Theresulting solution was stirred at room temperature for 24 hours. Thereaction was quenched by the addition of water (10 mL) and the organicphase was then washed with saturated copper sulphate (20 mL). Theaqueous phase was extracted with diethyl ether (3×20 mL) and thecombined organic extracts were washed with brine (50 mL) and dried overMgSO₄. The solvents were removed in vacuo and the crude product waspurified by flash column chromatography on silica, eluting with diethylether and dichloromethane (4:1) to furnish the title compound as finecolourless needles (497 mg, 74%); m.p. 69-71° C.; v_((max)) (KBr) 3409(O—H), 2979 (C—H), 1733 (C═O, lactone), 1718 (C═O, carbamate), 1646(C═O, amide) cm^(″1), δ_(H) (250 MHz, OMSO-d) 7.96-7.34 (13H, m, Fmoc×8and Ph×5), 7.90 (1H, d, /7.41 Hz, NH), 6.10 (1H, s, OH), 5.41-5.33 (1H,m, PhCH), 4.86 (1H, q, /6.76 Hz, CHCH₃), 4.40-4.24 (3H, m, OCH₂CH),4.16-4.07 (2H, m, CH₂OH), 3.79 (1H, q, /6.95 Hz, CHCH₃), 3.63 (1H, q,/6.65 Hz, CHCH₃), 1.44 (3H, d, /6.12 Hz, CHCH₃), 1.40 (3H, d, /7.19 Hz,CHCH₃), 1.27 (9H, s, C(CHg)₃), 0.90 (3H, d, /7.42 Hz, CHCH₃); δ_(c)(62.5 MHz, OMSO-d) 173.5, 171.3, 170.3, 156.6, 144.1, 141.1, 137.6,129.1, 128.7, 128.0, 127.6, 125.6, 121.7, 120.5, 80.2, 66.2, 60.9, 60.2,48.7, 47.4, 46.9, 27.8, 17.4, 17.1, 14.9; % (CL, NH₃), 775 (100%), 630(MH⁺, 25%), 485 (34%), and 408 (17%); HRMS for C₃₆H₄₄N₃O₇ requires630.3170. found 630.3166; [α]_(D) ²⁰ −41.2 (c 1.08 CHCl₃).

N-Acetyl-N-(1-phenyl-2-hydroxylethyl)alanyl-(S)-alamine tert-butyl ester

(3S,5R)-4-N-acetyl-3-methyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one(68) (220 mg, 0.94 mmol) and L-alanine tert-butyl ester (66) (205 mg,1.42 mmol, 1.5 equiv.) were dissolved in anhydrous dichloromethane (14mL) in a doubly sealed PTFE cylinder and subjected to ultra-highpressure of 19 kbar for 48 hours. After releasing the pressure, thesolution was filtered through a short pad of CELITE® diatomaceous earthand removal of solvent from the filtrate in vacuo yielded the crudeproduct which was purified by flash column chromatography on silicaeluting with diethyl ether and dichloromethane (4:1) to furnish thetitle product as fine colourless needles (120 mg, 34%); m.p. 38-40° C.;v_((max))(KBr) 3411 (O—H), 2980 (C—H), 1735 (C═O, lactone), 1646 (C═O,amide) cm⁻¹; δ_(H) (250 MHz, DMSO-d) 8.06 (0.5H, d, /6.95 Hz, NH×0.5),7.55-7.24 (5H, m, Ph), 6.54 (0.5H, d, J 6.38 Hz, NH×0.5), 5.82 (0.5H, t,/4.88 Hz, OH×0.5), 5.14-5.06 (1H, m, PhCH), 4.83 (0.5H, t, J 6.56 Hz,OH×0.5), 4.35 (0.5H, q, J 6.99 Hz, CH₃CH×0.5), 4.08-4.03 (2H, m, CH₂OH),3.98-3.76 (1.5H, m, CHCH₃×0.5 and CHCH₃×1), 2.23 (1.5H, s, COCH₃), 2.14(1.5H, s, COCH₃), 1.46-1.39 (12H, m, CHCH₃×3 and C(CH₃)₃×9), 1.19 (1.5H,d, /7.15 Hz, CHCH₃×1.5), 0.97 (1.5H, d, J 7.23 Hz, CHCH₃×1.5); δ_(c)(62.5 MHz, DMSO-d) 171.8, 171.7, 171.0, 170.8, 170.2, 140.0, 138.2,129.1, 128.2, 128.0, 126.8, 80.7, 62.7, 62.5, 60.8, 56.3, 53.4, 48.8,48.7, 27.9, 17.5, 16.9, 16.7, 15.2; m/z (CL, NH₃), 379 (MH⁺, 70%), 361(18%), 305 (20%), 249 (38%), 234 (100%), and 219 (40%); HRMS forC₂₀H₃₁N₂O₅ requires 379.2225 found 379.2240; [α]_(D) ²⁰ −37.0 (c 1.06CHCl₃).

N-Fmoc-(S)-alanyl-N-((1S)-phenyl-2-hydroxylethyl)-(R)-alanyl-(S)-alaninetert-butyl ester

To a solution of L-alanine tert-butyl ester (251 mg, 1.73 mmol, 3.0equiv.) in anhydrous dichloromethane (25 mL) was added trimethylaluminium (2.03 mL, 2.03 mmol 2 M in hexane, 3.5 equiv.) under anatmosphere of nitrogen. After 15 minutes,(3R,5S)—N—[N-Fmoc-(S)alanylj-3-methyl-5-phenyl˜3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one(280 mg, 0.58 mmol) in anhydrous dichloromethane (8 mL) was added. Theresulting solution was stirred at room temperature for 24 hours. Thereaction was quenched by the addition of water (7 mL) and the organicphase was then washed with saturated copper sulphate (15 mL). Theaqueous phase was extracted with diethyl ether (3×20 mL) and thecombined organic extracts were dried over MgSO₄. The solvent was removedin vacuo and the crude product was purified by flash columnchromatography on silica, eluting with petrol and diethyl ether (1:4) tofurnish the title compound as fine colourless needles (226 mg, 62%);m.p. 87-88° C.; v_((max))(KBr) 3410 (O—H), 2980 (C—H), 1727 (C═O), 1654(C═O) cm^(″1); δ_(H) (250 MHz, DMSO-d), 8.35 (0.5H, d, /6.18 Hz, NH)7.91-7.12 (13H, m, Fmoc×8 and Ph×5), 7.65 (0.5H, d, /7.14 Hz, NH), 7.55(0.5H, d, /7.32 Hz, NH), 6.39 (0.5H, d, /7.45 Hz, NH), 5.21-5.18 (0.5H,m, PhCH), 5.03-5.01 (0.5H, m, PhCH), 4.94-4.92 (0.5H, m, NHCHCH₃),4.80-4.78 (0.5H, m, NHCHCH₃), 4.65-4.62 (0.5H, m, NCHCH₃), 4.27-4.18(3.5H, m, OCH₂CH, and CH₂OH×0.5), 4.09-3.93 (2.5H, m, CH₂OH×1.5 andNHCHCH₃), 3.62-3.60 (0.5H, m, NCHCH₃×1), 1.44-1.36 (13.5H, s, (CEb)₃×9,CHCH₃×4.5), 1.23 (1.5H, d, /6.63 Hz, CHCH₃), 1.13 (1.5H, d, /7.35 Hz,CHCH₃), 0.92 (0.5H, d, /7.07 Hz, CHCH₃): δ_(c) (62.5 MHz. OMSO-d) 173.4,172.9, 171.9, 171.6, 169.7, 156.0, 144.2, 144.1, 141.1, 137.2, 129.0,128.3, 128.0, 127.7, 127.4, 127.3, 125.7, 120.5, 81.2, 80.8, 66.1, 61.6,55.3, 53.6, 48.6, 48.3, 47.5, 47.0, 27.9, 18.5, 18.2, 17.7, 17.1, 15.4;^(m)1_(z) (CL, NH₃), 775 (100%), 629 (M⁺, 36%), 457 (58%), 345 (27%),231 (33%) and 178 (100%); HRMS for C₃₆H₄₃N₃O₇ requires 629.3092. found629.3093; [α]_(D) ²⁰ +14.20 (c 1.15 CHCl₃).

L-Valine tert-butyl ester

To a mixture of sodium carbonate (1.20 g, 9.54 mmol, 5.0 equiv.) indeioned water (20 mL) and diethyl ether (20 mL) was added L-valinetert-butyl ester hydrochloride (400 mg, 1.71 mmol, 1.0 equiv.). Theresulting solution was stirred for 2 hours under an atmosphere ofnitrogen. The aqueous phase was extracted with diethyl ether (3×15 mL)and the combined extracts were dried over MgSO₄. The solvent was removedin vacuo to settle the title compound as colourless oil (320 mg, 97%);v_((max))(film) 3393 (N—H), 2967 (C—H), 1728 (C═O) cm^(″1); δ_(H) (250MHz, CDCl₃) 3.16 (1H, d, J 4.79 Hz, CHNH₂), 2.04-1.97 (1H, m, CH(CH₃)₂)1.47 (9H, s, (CH₃)₃), 1.38 (2H, s, NH₂), 0.97 (3H, d, /6.88 Hz,(CHg)₂CH×3), 0.90 (3H, d, J 6.86 Hz, (CH₃)₂CH×3); δ_(c) (62.5 MHz,CDCl₃) 175.3, 81.2, 60.7 32.6, 28.5, 19.7, 17.4; [α]_(D) ²⁰ +26.4 (cCHCl₃), (lit. [α]_(D) ²⁴ +25.3 (c 1.00 CHCl₃)).

N-Fmoc-(S)-a\any\-N-(1-phenyl-2-hydroxylethyl)-(5)-alanyl-(5)-valinetert-butyl ester (74)

To a solution of L-valine tert-hυiyl ester (161 mg, 0.93 mmol, 3.0equiv.) in anhydrous dichloromethane (10 mL) was added trimethylaluminium (0.55 mL, 1.09 mmol, 2 M in hexane, 3.5 equiv.) under anatmosphere of nitrogen. After 15 minutes,(3S,5R)—N—[N-Fmoc-(S)alanyl]-3-methyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one(150 mg, 0.31 mmol) in anhydrous dichloromethane (5 mL) was added. Theresulting solution was stirred at room temperature for 24 hours. Thereaction was quenched by the addition of saturated copper sulphate (20mL) and the mixture was extracted with diethyl ether (3×20 mL). Thecombined organic extracts were dried over MgSO₄. The solvents wereremoved in vacuo and the crude product was purified by flash columnchromatography on silica, eluting with diethyl ether and dichloromethane(9:1) to furnish the title compound as fine colourless needles (128 mg,63%); m.p. 75.0-76.0° C.; v_((max)) (KBr) 3411 (O—H), 2973 (C—H), 1718(C═O), 1654 (C═O) cm¹; δ_(H) (250 MHz, DMSO—O 7.96 (1H, d, /7.4 Hz, NH),7.97-7.29 (13H, m, Fmoc×8 and Ph×5), 5.43 (1H, br, OH), 5.35 (1H, t,/4.2 Hz, PhCH), 4.91 (1H, t, /6.8 Hz, CHCH₃), 4.43-4.40 (1H, m, OCH₂CH),4.31-4.21 (2H, m, OCH₂CH), 4.20-4.05 (2H, m, HOCH₂), 3.79-3.71 (1H, m,CHCH(CH₃)₂), 3.70-3.68 (1H, m, CHCH₃), 1.81-1.76 (1H, m, CH(CH₃)₂),1.46-1.34 (6H, m, CHCH₃×2) 1.31 (9H, s, f-butyl), 0.68-0.64 (6H, m,CH(CHg)₂); δ_(c) (62.5 MHz, OMSO-d) 173.1, 170.1, 170.0, 156.4, 144.2,141.1, 137.6, 129.1, 128.7, 128.3, 128.0, 127.4, 125.7, 124.5, 80.5,66.4, 63.2, 61.2, 58.1, 53.4, 47.1, 30.1, 27.9, 18.8, 18.4, 17.8, 15.1;^(m)1_(z) (CL, NH₃), 657 (M+34%), 579 (40%), 427 (59%), 363 (26%), and244 (100%); HRMS for C₃₈H₄₇N₃O₇ requires 657.3404. found 657.3398;[α]_(D) ²⁰ −38.7 (c 0.96 CHCl₃).

t-Butyl N—[(S)-2-hydroxy-1-phenylethyl]-(5)-valinyl-(5)-alanate

To a solution of L-alanine tert-butyl ester (180 mg, 1.24 mmol, 3.0equiv.) in anhydrous dichloromethane (10 mL) was added trimethylaluminium (0.56 mL, 1.12 mmol, 2 M in hexane, 2.7 equiv.) under anatmosphere of nitrogen. After 15 minutes,(3S,5R)-3-wopropyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (91mg, 0.41 mmol) in anhydrous dichloromethane (5 mL) was added. Theresulting solution was stirred at room temperature for 24 hours. Thereaction was quenched by the addition of saturated copper sulphate (15mL) and the mixture extracted with diethyl ether (3×15 mL). The combinedorganic extracts were dried over MgSO₄. The solvents were removed invacuo and the crude product was purified by flash column chromatographyon silica, eluting with petrol and diethyl ether (9:1 then 1:20) tofurnish the starting material (60 mg, 60%) and the title compound aslight yellow oil (50 mg, 33%); v_((max))(film) 3328 (O—H), 2977 (C—H),1733 (C═O, ester), 1651 (C═O, amide) cm^(″1); δ_(H) (250 MHz, CDCl₃)7.73 (1H, J 8.6 Hz, NH), 7.30-7.18 (5H, m, Ph), 4.54-4.78 (1H, m,CHCH₃), 3.74-3.68 (1H, m, PhCH), 3.59-3.50 (2H, m, HOCH₂), 2.79 (1H, d,74.8 Hz, CHCH(CH₃)₂), 1.97-1.93 (1H, m, CH(CH₃)₂), 1.41 (9H, s,t-butyl), 1.29 (3H, d, /8.7 Hz, CH₃), 0.81 (3H, d, J 4.4 Hz, CH(CH₃)₂),0.78 (3H, d, /4.4 Hz, CH(CH₃)₂); δ_(c) (62.5 MHz, CDCl₃) 174.0, 140.8,128.8, 128.1, 127.7, 125.9, 82.7, 67.6, 66.9, 64.6, 48.4, 31.8, 28.4,20.0, 19.2, 18.2, ^(m)1_(z) (CL, NH₃), 365 (MH⁺, 52%), 339 (29%), 333(76%), 291 (28%), 277 (100%) and 263 (10%); HRMS for C₂₀H₃₃N₂O₄ requires365.2432. found 365.2430. [α]_(D) ²⁰ −80.2 (c 0.98 CHCl₃).

Potassium N-benzylidenyl-(S)-valinate

To a solution of potassium hydroxide (958 mg, 17.10 mmol) in methanol(15 mL) was added L-valine (2.00 g, 17.10 mmol). The resulting solutionwas stirred under nitrogen for 3 hours. The solvent was removed in vacuobefore benzaldehyde (2.61 mL, 25.70 mmol 2.0 equiv.) in anhydrouspentane (30 mL) was added and the mixture was azeotropic distillatedunder nitrogen for 8 hours. The precipitate was collected and dried inhigh vacuo to furnish the title compound as a white solid (3.85 g, 93%),V(m_(ax)) (KBr) 2956 (C—H), 1594 (C═O) cm⁻¹; δ_(H) (250 MHz, OMSO-d),8.19 (1H, s, CH═N), 7.75-7.71 (2H, m, Ph×2), 7.44-7.40 (3H, m, Ph×3),3.26 (1H, d, J 7.24, CHCH(CH₃)₂), 2.21 (1H, m, CHCH(CH₃)₂), 0.86 (3H, d,J 6.72 Hz, CHCH(CH₃)₂×3), 0.79 (3H, d, /6.72 Hz, CHCH(CH₃)₂×3); δ_(c)(62.5 MHz, DMSO-d) 174.7, 159.0, 137.1, 130.3, 128.8, 128.1, 84.8, 31.4,20.8, 19.5.

N—[N-Fmoc-(S)-alanyl)]-3(S′)-isopropyl-5(R,S)-phenyl oxazolidinone

To the stirring suspension of potassium N-benzylidenyl-5-valinate (122mg, 0.50 mmol) in anhydrous dichloromethane (20 mL) was addedFmoc-L-alanine acid chloride (166 mg, 0.50 mmol) under nitrogen at 0° C.The resulting mixture was stirred for 4 hours at 0° C. and for another12 hours at room temperature. The solvent was removed in vacuo and thecrude product was purified by flash column chromatography on silica,eluting with petrol:diethyl ether (1:1) to furnish the title compound asfine colourless needles (174 mg, 70%); m.p. 69.0-71.5° C.; v_((maX))(KBr) 3400 (N—H), 2966 (C—H), 1802 (C═O, lactone), 1718 (C═O,carbamate), 1674 (C═O, amide) cm¹; δ_(H) (250 MHz, OMSO-d) 7.70-7.17(13H, m, Fmoc×8 and Ph×5), 6.45-6.43 (0.3H, m, PhCH×0.3), 5.36-5.28(0.7H, m, PhCH×0.7), 4.64-4.47 (1H, m, CHCH₃×0.7 and CHCH(CH₃)₂×0.3),4.47-4.09 (3H, m, CHCH₂), 4.01-3.82 (1H, m, CHCH₃×0.3 andCHCH(C₃)₂×0.7), 2.83-2.55 (0.3H, m, CH(CH₃)₂×0.3), 2.20-2.05 (0.7H, m,CH(CH₃)₂×0.7), 1.43-1.40 (3H, m, CHCH₃), 1.26-1.13 (3H, m, CH(CHs)₂×3)1.02-0.91 (3H, m, CH(CH₃)₂×3), 0.87-0.80 (3H, m, CHCH₃); δ_(c) (62.5MHz, CDCl₃) 177.5, 171.3, 169.5, 166.1, 156.0, 144.1, 141.7, 136.3,131.7, 130.6, 130.2, 129.1, 128.2, 127.5, 127.0, 125.5, 120.4, 91.5,70.2, 67.5, 61.8, 49.3, 47.5, 46.2, 34.2, 31.1, 30.7, 19.3, 18.9, 18.3,17.7, 16.7; % (Cl, NH₃), 498 (M⁺, 35%), 476 (47%), 463 (44%), 425 (23%),and 413 (100%); HRMS for C₃₀H₃₀N₂O₅ requires 498.2155. found 498.2151.

t-Butyl Fmoc-(S)-ala-(S)-val-(S)-alanate (79)

To a solution of L-alanine tert-butyl ester (114 mg, 0.78 mmol, 3.0equiv.) in anhydrous dichloromethane (10 mL) was added trimethylaluminium (0.46 mL, 0.91 mmol, 2 M in hexane, 3.5 equiv.) under anatmosphere of nitrogen. After 15 minutes,N—[N-Fmoc-(S)-alanyl)]-3(S)-wopropyl-5(R,S)-phenyl oxazolidinone (130mg, 0.26 mmol) in anhydrous dichloromethane (5 mL) was added. Theresulting solution was stirred at room temperature for 24 hours. Thereaction was quenched by the addition of saturated copper sulphate (20mL) and the mixture was extracted with diethyl ether (3×20 mL). Thecombined organic extracts were dried over MgSO₄. The solvents wereremoved in vacuo and the crude product was purified by flash columnchromatography on silica, eluting with petrol:diethyl ether (1:9) tofurnish the title compound as fine colourless needles (76 mg, 54%); mp153.0-155.0° C.; v_((max)) (KBr) 3292 (N—H), 2974 (C—H), 1734 (C═O,ester), 1696 (C═O, carbamate), 1645 (C═O, amide) cm^(″1); δ_(H) (250MHz, DMSO-d) 8.37 (0.5H, d, /6.42 Hz, NH), 8.18 (0.5H, d, 6.81 Hz. NH),7.95 (0.5H, d, J 7.56 Hz, NH×0.5), 7.63 (0.5H, d, /7.48 Hz, NH×0.5),7.96-7.35 (8H, m, Fmoc), 4.31-4.13 (5H, m, CHCH₃×2 and CHCH₂), 2.03 (1H,q, /6.57 Hz, CH(CH₃)₂), 1.42 (9H, s, f-butyl), 1.28-1.25 (6H, m, 2×CH₃)0.94-0.85 (6H, m, CH(CHb)₂); δ_(c) (62.5 MHz, DMSO-J) 173.1, 172.6,171.9, 170.8, 156.1, 144.1, 141.1, 128.0, 127.4, 125.6, 120.5, 80.7,66.0, 57.4, 57.0, 50.4, 48.7, 47.0, 31.5, 31.0, 30.8, 27.9, 19.5, 18.7,18.3, 17.9, 17.4, 17.2; ^(m)1_(z) (CL, NH₃), 537 (M⁺, 12%), 502 (100%),464 (50%), 426 (21%), and 414 (86%); HRMS for C₃₀H₃₉N₃O₆ requires537.2829. found 537.2836. [α]_(D) ^(°)−6.2 (c 0.57 CHCl₃).

N—[N-Fmoc-(S)-valinyl)]-3(S)-isopropyl-5(R,S)-phenyl oxazolidinone

To the stirring suspension of potassium N-benzylidenyl-(5)-valinate (123mg, 0.46 mmol) in anhydrous dichloromethane (20 mL) was addedFmoc-L-valine acid chloride (164 mg, 0.46 mmol) under nitrogen at 0° C.The resulting mixture was stirred for 4 hours at 0° C. and for another12 hours at room temperature. The solvent was removed in vacuo and thecrude product was purified by flash column chromatography on silica,eluting with petrol:diethyl ether (3:2) to furnish the title compound asfine colourless needles (183 mg, 75%); mp 76.0-78.0° C.; v_((max)) (KBr)3326 (N—H), 2966 (C—H), 1802 (C═O, lactone), 1722 (C═O, carbamate), 1663(C═O, amide) cm^(″1); δ_(H) (250 MHz, DMSO-d) 7.81-7.11 (14H, m, NH×1,Fmoc×8 and Ph×5), 6.4 (0.5H, s, PhCH×0.5), 4.98 (0.5H, s, PhCH×0.5),4.48-4.76 (5H, m, CHCH(CH₃)₂×2 and CHCH₂×3), 2.57-2.54 (1H, m,CH(CH₃)₂), 2.24-2.10 (1H, m, CH(CHs)₂), 1.28-0.63 (12H, m, CH(CH₃)₂×2);δ_(c) (62.5 MHz, DMSO-d) 170.3, 170, 169.7, 156.9, 144.1, 141.0, 137.5,130.9, 129.9, 129.5, 128.5, 128.0, 127.7, 127.4, 125.8, 120.5, 90.6,66.2 61.3, 60.9, 58.3, 46.9, 34.7, 32.6, 30.8, 30.3, 19.7, 18.7, 18.3,17.2, 16.7, 16.4; % (CL, NH₃), 526 (M⁺, 10%), 331 (40%), 230 (7%) and178 (100%); HRMS for C₃₂H₃₄N₂O₅ requires 526.2459. found 526.2466.

Tri-L-alanine

To a solution ofN-Fmoc-(S)-alanyl-N-((1R)-phenyl-2-hydroxylethyl)-(S)-alanyl-(S)-alaninetert-butyl ester (235 mg, 0.37 mmol) and tert-butanol (0.12 mL, 1.20mmol, 3.0 equiv.) in liquid ammonia (15 mL) and anhydroustetrahydrofuran (10 mL) was added lithium (23 mg, 3.70 mmol, 10.0equiv.) at −78° C. under an atmosphere of nitrogen. The resultingsolution was stirred until the blue colour was disappeared and thenwarmed to room temperature to evaporate all the liquid ammonia. Amixture of water (15 mL) and diethyl ether (10 mL) was added and theaqueous phase was extracted with diethyl ether (3×10 mL). Water wasremoved in vacuo and the crude product purified first by acidic ionexchange chromatography and then by flash column chromatography onsilica, eluting with methanol and water (7:3) to furnish the titlecompound as fine colourless needles (71 mg, 84%), v_((max))(KBr) 3276(N—H), 2985 (C—H), 1645 (C═O), 1592 (C═O), 1531 (C═O) cm^(″1); δ_(H)(250 MHz, D₂O), 4.53 (1H, q, /9.37, CH), 4.03 (2H, q, /7.22 Hz, CH×2),1.23 (3H, d, J 7.14, CH₃), 1.09 (3H, d, J 7.21, CH₃), 1.02 (3H, d, /7.24Hz, CH₃); δ_(c) (62.5 MHz. D₂O) 180.1, 173.9, 170.9, 51.3, 50.1, 49.2,17.7, 16.9, 16.7; ^(m)1_(z) (CL, NH₃), 231 (M⁺, 40%), 230 (100%), and228 (35%); HRMS for C₉H₁₇N₃O₄ requires 231.1215 found 231.1209; [α]_(D)²⁰ −72.8 (c 1.01 H₂O) (commercial one [α]_(D) 20^(D) −73.2 (c 1.02H₂O)).

(5S)-3-Methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one (35)⁶¹

(S)-2-phenylglycinol (3.00 g, 21.9 mmol, 1.0 equiv.) (34) and ethylpyruvate (2.67 mL, 24.1 mmol, 1 equiv.) were refluxed intrifluoroethanol (50 mL) over activated 4 molecular sieves (8.00 g) for24 hours. Filtration through a short pad of CELITE® diatomaceous earthand removal of solvent from the filtrate in vacuo delivered the crudeproduct which was purified by flash column chromatography on silica,eluting with petrol and diethyl ether (7:3) to furnish the titlecompound as a white solid (1.83 g, 44%); m.p. 70.0-71.0° C. (lit71.0-72.0° C.); v_((max))(KBr) 3007 (C—H), 1735 (C═O), 1640 (C═N) cm⁻¹;δ_(H) (250 MHz, CDCl₃) 7.45-7.32 (5H, m. Ph), 4.88-4.81 (1H, m, PhCH),4.56 (1H, dd, J 4.49 Hz, T 9.48 Hz, 6β-H), 4.25 (1H, dd J 13.01 Hz, T14.99 Hz, 6α-H), 2.41 (3H, s, CH₃); δ_(c) (62.5 MHz, CDCl₃) 160.7,155.9, 137.2, 129.4, 128.7, 127.5, 71.9, 60.1, 22.2; m/z (CL, NH₃), 189(M⁺, 25%), 159 (12%), 130 (24%), 104 (100%), 90 (21%), and 78 (6%); HRMSfor C₁₁H₁₁NO₂ requires 189.0787 found 189.0782. [α]_(D) ²⁰ +253.0 (c0.98 CHCl₃) (the enantiomer lit. [α]^(D20) −237.1 (c 1.11 CHCl₃)).

(3R,5S)-3-Methyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (36)

To a solution of (5S)-3-methyl-5-phenyl-5,6-dihydro-2H-1,4-oxazin-2-one(35) (1.70 g, 9.0 mmol, 1.0 equiv.) in anhydrous dichloromethane (60 mL)under an atmosphere of nitrogen was added PtO₂ (170 mg, 0.1 equiv.). Themixture was consecutively degassed and purged three times with hydrogenand then stirred for 5 hours under an atmosphere of hydrogen. Filtrationthrough a short pad of CELITE® diatomaceous earth and removal of solventfrom the filtrate in vacuo yielded the crude product which was purifiedby recrystallization from dichloromethane, diethyl ether and hexane tofurnish the title compound as a colourless needles (1.26 g, 74%); m.p.81.0-82.0° C. (lit. m.p. 81.0-82.0° C.); v_((max))(KBr) 3314 (N—H), 2981(C—H), 1736 (C═O), cm⁻¹, δ_(H) (250 MHz, CDCl₃) 7.43-7.26 (5H, m, Ph);4.42-4.23 (3H, m, CHCH₂), 3.88 (1H, q, /6.76 Hz, CHCH₃), 1.80 (1H, br.NH), 1.50 (3H, d, J 6.76 Hz, CH₃); δ_(c) (62.5 MHz, CDCl₃) 170.7, 138.1,129.3, 129.1, 127.5, 75.4, 58.2, 55.4, 19.0; m/z (CL, NH₃), 192 (MH⁺,30%), 147 (68%), 132 (64%), 104 (100%), and 91 (10%); HRMS for C₁₁H₁₃NO₂requires 192.1025 found 192.1019. [α]_(D) ²⁰ +88.8 (c 0.96 CHCl₃) (lit.[α]_(D) ²⁰ +92.3 (c 0.84 CHCl₃)).

(3R,5S)—N—[N-Fmoc-(S)alanyl]-3-methyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one(37)

To a vigorously stirred mixture of(3R,5S)-3-methyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one (36)(500 mg, 2.62 mmol), Na₂CO₃ (1.40 g, 13.3 mmol, 5.0 equiv.) in 1:1dichloromethane and water (40 mL) was added N-Fmoc-L-alanine acidchloride (1.04 g, 3.14 mmol, 1.2 equiv.) in dichloromethane (10 mL)dropwise over 5 min. The resulting solution was stirred for 2 hours. Theaqueous phase was extracted with dichloromethane (3×15 mL). The combinedextracts were washed with saturated Na₂CO₃ (50 mL), water (2×30 mL),brine (50 mL) and dried over MgSO₄. The solvents were removed in vacuoand the crude material was purified by flash column chromatography onsilica, eluting with petrol and diethyl ether (1:4) to furnish the titlecompound as fine colourless needles (1.02 g, 80%); m.p. 87-88° C.;v_((max)) (KBr) 3323 (N—H), 2982 (C—H), 1761 (C═O, lactone), 1717 (C═O,carbamate), 1656 (C═O, amide) cm^(″1); δ_(H) (400 MHz, DMSO-J, 110° C.)7.84-7.29 (13H, m, Fmoc×8, Ph×5), 7.08 (1H, br, NH), 5.54 (1H, t, /5.88Hz, PhCH), 4.96 (1H, q, /7.11 Hz, NCHCH₃); 4.68-4.60 (2H, m, PhCHCH₂),4.41-4.32 (3H, m, CHCH₃NH×1, OCH₂CH×2), 4.22 (1H, t, /6.72 Hz OCH₂CH),1.45 (3H, d, /7.15 Hz₅ NCHCH₃), 1.08 (3H, d, /6.71 Hz, CHCH₃NH); δ_(c)(62.5 MHz, OMSO-d) 174.0, 172.8, 170.4, 169.6, 156.3, 144.1, 141.1,137.7, 129.4, 128.7, 128.0, 127.4, 127.3, 127.1, 125.6, 120.5, 68.8,66.0, 55.5, 55.3, 52.2, 51.4, 50.0, 47.2, 20.5, 18.6, 17.7, 17.1; ′7_(z)(C.I., NH₃), 485 (MH⁺, 12%), 431 (8%), 381 (7%), 281 (15%) and 149(100%); HRMS for C₂₉H₂₉N₂O₅ requires 485.2069. found 485.2076; [α]_(D)²⁰ +22.2 (c 0.94 CHCl₃).

N-Fmoc-(S)-alanyl-N-((1S)-phenyl-2-hydroxylethyl)-(R)-alanyl-(S)-alaninetert-butyl ester (71)⁴⁸

To a solution of L-alanine tert-butyl ester (66) (251 mg, 1.73 mmol, 3.0equiv.) in anhydrous dichloromethane (25 mL) was added trimethylaluminium (2.03 mL 2.03 mmol, 2 M in hexane, 3.5 equiv.) under anatmosphere of nitrogen. After 15 minutes,(3R,5S)—N—[N-Fmoc-(S)alanyl]-3-methyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one(37) (280 mg, 0.58 mmol) in anhydrous dichloromethane (8 mL) was added.The resulting solution was stirred at room temperature for 24 hours. Thereaction was quenched by the addition of water (7 mL) and the organicphase was then washed with saturated copper sulphate (15 mL). Theaqueous phase was extracted with diethyl ether (3×20 mL) and thecombined organic extracts were dried over MgSO₄. The solvent was removedin vacuo and the crude product was purified by flash columnchromatography on silica, eluting with petrol and diethyl ether (1:4) tofurnish the title compound as fine colourless needles (226 mg, 62%);m.p. 87-88° C., v_((max)) (KBr) 3410 (O—H), 2980 (C—H), 1727 (C═O), 1654(C═O) cm¹, δ_(H) (250 MHz, OMSO-d), 8.35 (0.5H, d, /6.18 Hz, NH)7.91-7.12 (13H, m, Fmoc×8 and Ph×5), 7.65 (0.5H, d, /7.14 Hz, NH), 7.55(0.5H, d, /7.32 Hz, NH), 6.39 (0.5H, d, /7.45 Hz, NH), 5.21-5.18 (0.5H,m, PhCH), 5.03-5.01 (0.5H, m, PhCH), 4.94-4.92 (0.5H, m, NHCHCH₃),4.80-4.78 (0.5H, m, NHCHCH₃), 4.65-4.62 (0.5H, m, NCHCH₃), 4.27-4.18(3.5H, m, OCH₂CH, and CH₂OH×0.5), 4.09-3.93 (2.5H, m, CH₂OH×1.5 andNHCHCH₃), 3.62-3.60 (0.5H, m, NCHCH₃×1), 1.44-1.36 (13.5H, s, (CHa)₃×9,CHCH₃×4.5), 1.23 (1.5H, d, /6.63 Hz, CHCH₃), 1.13 (1.5H, d, /7.35 Hz,CHCH₃), 0.92 (1.5H, d, /7.07 Hz, CHCH₃); 6, (62.5 MHz, OMSO-d) 173.4,172.9, 171.9, 171.6, 169.7, 156.0, 144.2, 144.1, 141.1, 137.2, 129.0,128.3, 128.0, 127.7, 127.4, 127.3, 125.7, 120.5, 81.2, 80.8, 66.1, 61.6,55.3, 53.6, 48.6, 48.3, 47.5, 47.0, 27.9, 18.5, 18.2, 17.7, 17.1, 15.4;% (CL, NH₃), 775 (100%), 629 (M⁺, 36%), 457 (58%), 345 (27%), 231 (33%)and 178 (100%); HRMS for C₃₆H₄₃N₃O₇ requires 629.3092. found 629.3093;[α]_(D) ²⁰ +14.20 (c 1.15 CHCl₃).

LDL-alanine

To a solution ofN-Fmoc-(S)-alanyl-N-((1R)-phenyl-2-hydroxylethyl)-(R)-alanyl-(S)-alaninetert-butyl ester (235 mg, 0.37 mmol) and tert-butanol (0.12 mL, 1.20mmol, 3.0 equiv.) in liquid ammonia (15 mL) and anhydroustetrahydrofuran (10 mL) was added lithium (23 mg, 3.70 mmol, 10.0equiv.) at −78° C. under an atmosphere of nitrogen. The resultingsolution was stirred until the blue colour disappeared and then allowedto warm to room temperature to evaporate off the liquid ammonia. Amixture of water (15 mL) and diethyl ether (10 mL) was added and theaqueous phase was extracted with diethyl ether (3×10 mL). Water wasremoved in vacuo and the crude product purified first by acidic ionexchange chromatography and then by flash column chromatography onsilica, eluting with methanol and water (7:3) to furnish the titlecompound as fine colourless needles.

To a solution of(3S,5R)—N—[N-Fmoc-(S)alanyl]-3-methyl-5-phenyl-3,4,5,6,-tetrahydro-2H-1,4-oxazin-2-one(33) (1.00 g, 2.06 mmol, 1.0 equiv.) in anhydrous tetrahydrofuran (40mL) was added 1,8-diazabicyclo[5.4.0]-undec-7-ene (0.03 mL, 0.21 mmol,0.1 equiv.) under an atmosphere of nitrogen. The resulting solution wasstirred at room temperature for 3.5 hours beforeN,N-diisopropylethylamine (0.40 mL, 2.26 mmol, 1.1 equiv.),N-Fmoc-L-alanine (0.76 g, 2.46 mmol, 1.2 equiv.) andbromotripyrrolidinophosphonium hexafluorophosphate (1.21 g, 2.46 mmol,1.2 equiv.) were added. The resulting solution was stirred for another18 hours during which time a white precipitate was formed. The mixturewas filtered through a short pad of CELITE® diatomaceous earth andremoval of solvent from the filtrate in vacuo yielded the crude productwhich was purified by flash column chromatography on silica, elutingwith dichloromethane and diethyl ether (3:7) to furnish the titleproduct as a white powder (0.96 g, 86%); m.p. 100.0-101.0° C.;v_((max))(KBr) 3311 (N—H), 2981 (C—H), 1741 (C═O), 1718 (C═O), 1647(C═O) cm⁻¹; δ_(H) (250 MHz, DMSO-d) 7.79 (1H, /6.70 Hz, NH), 7.68-7.07(13H, m, Fmoc×8, Ph×5), 7.32 (1H, J 7.85 Hz, NH), 5.27 (1H, br, PhCH),5.16-4.96 (1H, m, PhCHCH₂×1), 5.16-4.96 (1H, m, PhCHCH₂×1), 4.64-4.62(1H, m, CHCH₃), 4.55-4.51 (1H, m, CHCH₃), 4.35-4.32 (1H, m, OCH₂CH),4.00 (2H, m, OCH₂CH), 3.89-3.80 (1H, m, CHCH₃), 0.98 (3H, d, J 13.92 Hz,CHCH₃), 0.93 (3H, br, CHCH₃), 0.62 (3H, d, /6.89 Hz, CHCH₃); δ_(c) (62.5MHz, DMSO-d) 172.8, 171.6, 170.0, 156.0, 144.2, 141.1, 136.3, 128.9,128.3, 128.0, 127.4, 126.8, 125.7, 120.4, 69.1, 66.0, 52.9, 50.6, 49.9,47.0, 30.8, 20.9, 18.5, 17.8; m/z (CL, NH₃) 231 (M⁺, 40%), 230 (100%),and 228 (35%); HRMS for C₃₂H₃₃N₃O₆ requires 555.2369 found 231.1209;[α]_(D) ²⁰ −31.3 (c 0.90 CHCl₃).

To a solution of(3S,5R)—N—[N-Fmoc-(S)alanyl-(S)-alanine]-3-methyl-5-phenyl-3,4,5,6-tetrahydro-2H-1,4-oxazin-2-one(49) (114 mg, 0.206 mmol, 1.0 equiv.) in anhydrous tetrahydrofuran (5mL) was added 1,8-diazabicyclo[5.4.0]-undec-7-ene (0.015 mL, 0.103 mmol0.5 equiv.) under an atmosphere of nitrogen. The resulting solution wasstirred at room temperature for 5 hours before N,N-diisopropylethylamine(0.026 mL, 0.144 mmol, 0.7 equiv.), N-Fmoc-L-alanine (76 mg, 0.246 mmol,1.2 equiv.) and bromotripyrrolidinophosphonium hexafluorophosphate(0.121 g, 0.246 mmol, 1.2 equiv.) were added. The resulting solution wasstirred for another 19 hours during which time a white precipitate wasformed. The mixture was filtered through a short pad of CELITE®diatomaceous earth and removal of solvent from the filtrate in vacuoyielded the crude product which was purified by flash columnchromatography on silica, eluting with dichloromethane and acetone (7:3)to furnish the title product as a white powder. (89 mg, 68%); m.p.118.0-120.0° C.; v_((max))(KBr) 3316 (N—H), 2985 (C—H), 1738 (C═O), 1708(C═O), 1647 (C═O) cm⁻¹; δ_(H) (250 MHz, DMSO-d) 8.00 (1H, d, /7.28 Hz,NH), 7.91-7.30 (13H, m, Fmoc×8, Ph×5), 7.52 (1H, d, /7.58 Hz, NH), 5.48(1H, br, PhCH), 5.32-5.02 (1H, m, PhCHCH₂), 4.88-4.85 (1H, m, CHCH₃),4.74-4.69 (1H, m, CHCH₃), 4.56 (1H, br, OCH₂CH), 4.26-4.27 (2H, m,OCH₂CH), 4.03 (1H, t, /7.25 Hz, CHCH₃), 3.63-3.58 (0.5H, m, CHCH₃),3.14-3.12 (0.5H, m, CHCH₃), 1.26-0.97 (12H, m, CHCH₃×4); δ_(c) (62.5MHz, DMSO-d) 172.5, 172.2, 171.6, 170.0, 156.0, 144.2, 141.1, 136.5,128.9, 128.3, 128.0, 127.4, 126.7, 125.7, 120.5, 65.9, 56.2, 53.9, 53.0,47.9, 46.0, 42.2, 32.5, 31.0, 29.9, 18.5, 17.8, 17.1, 12.9; % (CL, NH₃);HRMS for C₃₅H₃₈N₄O₇, requires 626.2741 found; [α]_(D) ²⁰ −27.2 (c 1.04acetone).

¹H-NMR data obtained for Tri-L-alanine made according to the inventionwith commercial tri-L-alanine was compared with excellent results.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A process for the production of a compound of formula (Ic):

comprising reaction of a compound of formula (VII)

with a compound of formula (III)HY—R⁷  (III) wherein X is O, S, or NR⁸, where R⁸ is C₁₋₁₆ alkyl, C₆₋₁₂aryl or hydrogen; Y is O, S or NH; R² is independently selected from aC₁₋₁₀ branched or straight chain alkyl group, C₅₋₁₂ heteroaryl group orC₆₋₁₂ aryl group, optionally substituted with OR¹³, SR¹³, N(R¹³)₂,CO₂R¹³, CON(R¹³)₂, SO₂R¹², SO₃R¹², phenyl, imidazolyl, indolyl,hydroxyphenyl or NR¹³C(═NR¹³)N(R¹³)₂; wherein each R^(1′) isindependently hydrogen or as defined from R¹ below; R¹⁴ is—[CO—C(R^(1′))(R⁹)—N(R¹⁰)]_(m)—(R¹¹); R¹² is hydrogen, C₁₋₆ alkyl, C₆₋₁₂aryl or N(R¹³)₂, wherein each occurrence of R¹³ is independentlyhydrogen, C₁₋₆ alkyl or C₆₋₁₂ aryl, each R⁹ and R¹⁰ is independentlyhydrogen or a group as defined for R^(1′); or R⁹ and R¹⁰ can togetherform a 4 to 7 membered ring, optionally substituted with OR¹³, SR¹³,N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, C₁₋₁₀ alkyl or C₆₋₁₂ aryl, wherein said ringcan be fully, partially or unsaturated, and wherein the ring may containone or more heteroatoms selected from O, S or N; R¹¹ is hydrogen or anamino protecting group, wherein the amino protecting group is abenzyloxycarbonyl group, a t-butoxycarbonyl group, a2-(4-biphenylyl)-isopropoxycarbonyl group, a fluorenylmethoxycarbonylgroup, a triphenylmethyl group or a 2-nitrophenylsulphenyl group; R⁵ isa C₅₋₁₂ aryl, C₅₋₁₂ heteroaryl or C₁₋₈ branched or straight chain alkyloptionally substituted with OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂,phenyl, imidazolyl, indolyl, hydroxyphenyl or NR¹³C(═NR¹³)N(R¹³)₂ or alinker for attachment of formula (VII) to a resin, wherein the linker isOR¹³, N(R¹³)₂, CO₂R¹³ or SR¹³, or an alkyl group having 1 to 4 carbonsor a C₆₋₁₂ aryl group, said alkyl and aryl groups being optionallysubstituted with OR¹³, N(R¹³)₂, CO₂R¹³ or SR¹³; R⁶ is hydrogen or

wherein R⁵ and X are as defined above; R⁷ is a group

or is independently selected from a C₁₋₁₀ branched or straight chainalkyl group or a C₆₋₁₂ aryl group, optionally substituted with OR¹³,SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, SO₂R¹², SO₃R¹², phenyl, imidazolyl,indolyl, hydroxyphenyl or NR¹³C(═NR¹³)N(R¹³)₂ or wherein R⁷ and Ytogether form a 4 to 7 membered ring, optionally substituted with OR¹³,SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, SO₂R¹², SO₃R¹², phenyl, imidazolyl,indolyl, hydroxyphenyl or NR¹³C(═NR¹³)N(R¹³)₂, wherein said ring can befully, partially or unsaturated, and wherein the ring may contain one ormore heteroatoms in addition to Y, selected from O, S or N; wherein R¹is independently selected from a C₁₋₁₀ branched or straight chain alkylgroup, C₅₋₁₂ heteroaryl group or C₆₋₁₂ aryl group optionally substitutedwith OR¹³, SR¹³, N(R¹³)₂, CO₂R¹³, CON(R¹³)₂, SO₂R¹², SO₃R¹², phenyl,imidazolyl, indolyl, hydroxyphenyl or NR¹³C(═NR¹³)N(R¹³)₂; R⁴ is acarboxyl protecting group or hydrogen, wherein the carboxyl protectinggroup is methyl, ethyl, benzyl, t-butyl or phenyl; n is 1, 2 or 3, and mis a value selected from 1-100.
 2. The process as claimed in claim 1wherein R¹ and R² are independently selected from C₁ alkyl optionallysubstituted with OH, SH, CO₂H, CONH₂, phenyl, imidazolyl, indolyl orhydroxyphenyl; C₂ alkyl optionally substituted with OH, CO₂H, CONH₂ orSCH₃; C₃ alkyl NHC(═NH)NH₂ or C₄ alkyl optionally substituted with NH₂.3. The process as claimed in claim 1 wherein R⁵ is a linked resin andthe process is carried out on solid phase.
 4. The process as claimed inclaim 1 wherein the process is carried out in solution.
 5. The processas claimed in claim 1, further comprising replacement of the R⁶ groupwith hydrogen to form a compound of formula (Ic):

wherein X, Y, R², R⁷ and R¹⁴ are as defined above in claim 1, andwherein R⁶ is hydrogen.
 6. The process as claimed in claim 1 wherein theproduction of a compound of formula (Ic) occurs without epimerization.7. The process as claimed in claim 1, wherein the production of acompound of formula (Ic) comprises (a) converting an amine of formula(IV)

to form a compound of formula (VII) via peptide bond formation; and (b)reacting the compound of formula (VII)

with a compound of formula (III).
 8. The process of claim 7, wherein theformation of a compound of formula (VII) occurs by reaction of one ormore compounds of formula (V)Z—CO—R³  (V) in a stepwise manner, wherein R³ is as defined for R² or ishydrogen, or a group

or a group —C(R^(1′))(R⁹)—N(R¹⁰)(R¹¹); Z is hydroxide, halide or azide;R^(4′) is as defined for R⁴; and wherein Y, R^(1′), R⁴, R⁹, R¹⁰ and R¹¹are as defined above in claim
 1. 9. The process as claimed in claim 7,wherein the production of a compound of formula (Ic) occurs withoutepimerization.
 10. The process as claimed in claim 7, wherein R⁵ is alinked resin and the process is carried out on solid phase.
 11. Theprocess as claimed in claim 7, wherein the process is carried out insolution.